Abortion: 10 years as an atheist and I still don't get it

[FlatAssembler]

Belacqua
it's unethical to force a woman to carry a fetus if she doesn't want to.

Suppose the father doesn't want to pay to support the child after it's born. Is it ethical for the government to force him to pay? 

How do we decide when a parent should be forced to support and when he or she shouldn't be forced?

Well, I think it's unethical for a government to force a father to pay alimentation. Unless the father stole the money from the mother. The father might have legitimate reasons for refusing to pay. Maybe he needs that money more than the mother does, maybe he needs that money to pay for his medication which he will die if he doesn't manage to pay. The government can't be expected to always have the information it needs to make such decisions.