I've been covering pacifism, just war, suicide, euthanasia, cloning, abortion, and capital punishment in my classes, and I've been thinking a lot about the "playing God" argument that arises in all these issues. It also plays a major role in arguments against contraception, which Wink and I treated not too long ago. What exactly is this argument supposed to amount to? The one underlying feature to the different versions I can think of is that somehow God has given us certain responsibilities to do but has withheld from us certain things to do, and it's playing God to do the latter. But which things would those be, and why those things? The different realms God is said to have exclusive rights over have been anything involving when someone might die or come into being, any way to affect the characteristics of someone as they come into being, and other issues related to life and death. A helpful analogy, though, is to consider groups like the Amish who make this argument not just about life and death but about many ways in which we live our life. They apply it to certain kinds of technology, though I've never been able to find a consistent standard behind their choices of which kinds of technology to use and which not to use. Knitting needles and computers are equally human-developed technology. But those of a more moderate persuasion who will still give such an argument seem to me to limit it to these life and/or death issues and to using technology to modify something seen to be fundamental to God's prerogative in giving and taking life (and determining what form such life will take, which is why cloning and genetic engineering are part of this).
One version of this argument might be called the natural law version. Certain actions are against nature, either because God created nature with built-in purposes or because of some other reason that should lead us to honor nature (e.g. the Stoics considered nature to be God and had some natural law inclinations). I'm very much in favor of the idea that God created things with certain purposes in mind. I don't think we can just read off nature what those purposes are, and no Christian who takes the Bible seriously should. You see, there's this thing called the fall, which Christians have always taken to have damaged all of creation. The fallen realm is thus no guide to morality for a Christian. [Incidentally, those who use natural law as an argument against homosexuality don't think the way Paul did when he wrote Romans 1:18ff., since that passage is about how homosexuality is a natural result of the fall.]
The general point here will apply without appeal to Christianity. The main point is that how things are does not entail how things ought to be in the sense that things in nature are often a bad model for our actions, and we do lots of things that aren't natural but that we normally and rightly think are just fine (e.g. building houses, concocting medicinal treatments for illnesses, churning butter, irradiating food in a microwave oven, and recording sound waves in digital or analog format for later playback).
Now one might argue that only certain kinds of unnatural things are to be avoided, and the kinds I listed above are ok. My question will be how we determine which. If we turn to moral considerations, then we're back to square one, wondering which ones are moral or non-moral and which are immoral. We can decide that based on independent moral principles, but then we'll need to give other moral arguments. The "playing God" argument has ceased to be a moral argument itself, as it was supposed to be. It's just a substitute for giving a moral argument, which therefore makes it mere rhetoric. I want an argument, and we might as well just focus on the argument and avoid talk of playing God if that's what we're up to.
There are a couple ways to explain the difference between unnatural things that God has allowed and unnatural things God has forbidden. One is through scripture, but then we're back to scriptural arguments rather than "playing God" as an argument in itself, and we have the same problem as before, with this label turning out to be mere rhetoric. Christians might give arguments against contraception based on scriptural principles, but then saying that a further reason is that contraception is playing God really adds nothing to the argument already given. It's mere rhetoric. This way of distinguishing between the two is also useless in any case in which the revelation of God is silent, which includes far too many cases for me to want to be confident that many practices claimed to be playing God really are bad.
The one area where much of this kind of talk arises, as I said at the beginning, is with life and death issues, which suggests one possible non-trivial distinction between the good and bad kinds of unnaturalness without appealing directly to divine revelation. That's that God has a divine prerogative over life and death, and if we do anything to affect when or how someone might be born or die, we've done something only God has the prerogative to do. If we leave it just at that, we get ridiculous results. We wouldn't be able to use the abilities God has given us to develop things like medicine. It would be wrong to save someone's life by slamming on your brakes when they cross the road in front of your car. For that matter, eating healthier or exercising to try to maximize your time for effectiveness in this life would be pretty downright awful. How could someone play God like that with the length of their life?
I'm not sure how best to modify the view to make it less crazy. It must have something to do with certain kinds of not using technology to alter how things normally go with life and death without limiting other uses of technology to alter how things normally go with life and death, but it must be certain issues of life and death and not others, or we get the results at the end of the last paragraph. So which issues matter? Why would it be wrong to use technology to make it less likely that you will conceive? Why is it wrong to use technology to aid reproduction, say by using hormones to make your body do what it's supposed to do naturally? In both cases, it can't be merely that God has a prerogative over life and death, because I've listed some perfectly good things, even morally excellent things, that involve making decisions about life and death.
There are some things that I think are genuinely wrong that people call playing God, but I don't think that's an argument for why they're wrong. For example, I think it's a really bad idea to kill human organisms to get stem cells for research, but I have moral reasons against doing that. It's wrong to use someone as a means to an end, for instance. I also think it's a very bad idea to pursue what they're calling cloning of human beings (which is really just massive genetic engineering of an already existing human organism created by in vitro fertilization). The main reason is that no one has any thought about how to avoid the problem that a clone developed from my DNA would have a natural lifespan of the rest of my natural life and thus would be robbed of 30 years. Another fairly important reason is the huge number of embryos and spontaneous abortions that would be necessary to have one clone survive and reach birth. A third reason is that you're taking an existing human life and obliterating its genetic code to do it. None of my opposition to cloning has to do with any notion of playing God. I don't think that's a real argument, and therefore I don't think cloning in principle is wrong at all. It's just a bad idea to do anything that has the features I've listed. If they can remove those elements, I don't see any problem with using technology to create a human being that has my exact genetic code. The playing God argument adds nothing to the discussion, since it's really just a placeholder for not having any argument.
One advantage cloning has that other forms of genetic engineering don't is that you know what the result of your tinkering will look like, at least roughly speaking. Some changes occur during pregnancy, and some genes don't turn on due to environmental conditions, so just as identical twins aren't exact duplicates so too this kind of identical twin isn't an exact duplicate, but it's close enough to know that you haven't combined some genes in a disastrous way. When we alter the genetic structure of a living organism and then let it develop, we might know some of the effects, but we don't truly know much of what will happen. According to my wife, who has a piece of paper saying she learned a lot of biology, they've put cold-water fish genes in tomatoes to make them survive better in the cold, but they don't taste as good. Modifying foods to resist herbicides might lead to cross-pollinization to other plants in the wild who then will resist herbicides themselves. People have all sorts of speculative worries about genetic modifications causing food allergies, though they don't take into account the fact that people with food allergies used to die but now survive due to better health care, which satisfactorily explains the higher rate of such allergies now. Still, paranoid people are sometimes on to something, and we don't really know what the effects of some of these modifications could be. It's one thing to do the kind of genetic engineering Jacob did in Genesis, which was really just selective breeding. It's just as much genetic engineering as what they do now, since it has the same goal and has methods to modify the population genetically to achieve that end. The kind of genetic engineering we now have, though, might have more serious consequences that are at least reason to be cautious. This is merely because of our lack of knowledge, though. That's the reason it's bad.
This may well be the only kind of playing God argument with some substance. If our ignorance really limits our imagination as to what might happen, then we're guilty of using science to do things we don't have any business trying to do. Anyone working on splitting the atom who was kidding themselves into thinking this could only benefit society was playing God in this sense. It's not because it's playing God to use the vast power released when splitting an atom. It's because it's playing God to use that power while not considering what other powerfully negative consequences doing such things could lead to. It's acting as if we're omniscient, in other words (not acting as if we're omnipotent, which is more what people who use the playing God argument might be more inclined to think). I suppose if someone were to pretend to be omnipotent, that would be playing God, but that's not what happens when we use our limited abilities to do things within the limits of those abilities. The thing that should restrict our actions should be moral considerations and not trying something we're incapable of. Simply saying something is playing God adds nothing to the discussion and really does seem to me to be mere rhetoric, unless it's a point about our limited knowledge, which can effectively be made without using such unclear terminology. If there's an argument, give it. If not, don't act as if there's something wrong with something by calling it playing God. That doesn't count as a real argument, and it's always bad to use a pseudo-argument simply because you don't have a real one.
Update: The final post in Bonnie's excellent series on contraception at Off the top gets at a number of issues, but one of them is essentially the worry I've been raising here for "playing God" arguments.