Why would anyone risk conceiving a child who could easily end up as an enemy of God being tormented for eternity?
I think the answer must be, for the Christian, that God ordained a world in which that possibility exists, and he brought that world into being anyway. In other words, when the world was created, God did that. God created a world in which many would be lost.
So this question becomes, "Why would anyone join God in that process?"
The bottom line is going to be, Because we trust God. We believe in God. We take our cues from God and not our own mere logic.
I don't despise this question. I don't minimize this question. Under "Trust in God," the two answers are,
1) If someone perishes, then it will be just that they perish, not unjust. They will deserve to perish. And in their perishing God's justice will be glorified. His wrath will be displayed, according to Romans 9:20-21. And the lostness of the person will, in fact, serve God's ultimate good purposes for the glorification of his name and the good of his elect.
2) The prospect of someone being saved and enjoying God forever and ever is so great. Why wouldn't you want to conceive as many babies as you could? The horrors of hell are not as horrible as the glories of heaven.
So this question should have it's counterpart: "If it's possible that a human being could be brought into existence who would know the living God and spend an eternity in ever-increasing joy, why wouldn't you want to have as many babies as possible?"