As the discussion at Jollyblogger continues on the five points of Calvinism, one of the commenters on Total Depravity and Free Will (which I discussed briefly the other day) gives an argument I've heard many times, that Calvinism leads to universalism. The idea here is that if God can save people by causing them to believe, and it doesn't violate their freedom in any moral way to do so (which compatibilism assumes), then God must have the obligation to save all. God has the ability to do something good with no moral reason not to and even a compelling moral reason to do it. Thus Calvinist principles require God to save everyone.
Another commenter responds with something that really clarified for me what's wrong with this argument. The commenter says that a similar argument can be constructed based on God's justice, arguing that God ought to damn everyone to hell, and anything that might move God away from such a decision is really unjust and therefore morally evil. The first argument ignores God's justice while emphasizing God's mercy, and this second argument ignores God's mercy while emphasizing God's justice. That's how the commentator put it, anyway. I would say, rather, that each argument, rather than ignoring one of God's attributes, instead redefines one of the two attributes so as to preclude the other. Universal salvationists define mercy as all-encompassing and inconsistent with the kind of justice the Bible attributes to God. Universal damnationists define justice as all-encompassing and inconsistent with the kind of mercy the Bible attributes to God. Both make God in human image, because only we have such diminished justice as to be without possibility of mercy, and only we have such diminished mercy as to be without possibility of justice. I should add that similar arguments about annihilationism vs. conscious torment in hell can fall into the same pitfalls, on both sides of the debate.