I had been planning on writing a post on contraception, but Jeremy has beat me to it. His post is excellent and there is little that he says there that I would disagree with. I do want to add some of my own point of view so here goes:
In my circles, I have come across several people who believe that using contraception demonstrates a lack of faith in God. Some have been aware of my infertility, one even had infertility issues of her own. The universal refrain among them was that to use contraception was try to control our lives too much instead of allowing God to have control.
What irks me is that all of them also had financial planners and invested heavily in their retirement funds. Financial planning was defended under the rubric of "stewardship", while family planning was attacked under the rubric of "unfaithfulness".
Admittedly, family planning can be done in an unfaithful manner. And financial planning can be done as proper stewardship. But not all family planning is unfaithful, sometimes it is good stewardship. In the same way, some financial planning is not good stewardship but unfaithfulness.
When pressed to defend their anti-contraception stance, they would ususally fall back on the "be fruitful and multiply, and fill the earth" command. I actually had a family member, one with whom I had shared the hardest parts of my infertility struggles, telling me that everyone, me included, had a moral imperative to multiply. For me not to do so was apparently a sin, even though I had no control over it. (To his credit, he did not put it quite so bluntly and apologised immediately after I told him how hurt I was. Apparently, he also later changed his mind on the issue, or so I gathered by his vasectomy.)
This was of course ridiculous. The command to be fruitful and multiply hardly applies to all people in all circumstances.
The variant of this arguement that I have been coming across recently is that we need to have more children because we need a larger working class in order to support the retired elderly. Population control (and by extention, contraception) is seen as a moral evil because certain institutions, like Social Security, won't work properly if the elderly outnumber the tax base.
Of course, the logical end of this, especially as you factor in increasing life-spans, is that the population must grow exponentially forever. There are some practical problems involved with this. [Examples are left as an excercise for the reader.]
Coming back to the "be fruitful and multiply, and fill the earth" command--have we ever considered that maybe we've completed this command? Maybe we've already filled the earth? I know that we can certainly fit more people on this planet, and that the planet could certainly support more of us than it does currently, but is that the right criteia by which to measure if we have filled the earth? The rest of the command is to "subdue the earth", which I take to me that we are to steward and cultivate the earth. It may be that we are to fill the earth until we are numerous enough to do such a job properly. I would contend that we curently have enough people to do that. (And if you take a more conservative view of the word "subdue" and take it to mean "control and subjugate", then we have more than enough to do that--witness the mass extinctions going on around us.)
So if that is the case and we have fulfilled the command, then even as a species do we any longer have any moral imperative to procreate? This is of course not to say that we shouldn't procreate; I'm just questioning if our species any onger has a moral imperative to increase our population.