re: if women can abort their children, why can't men opt out of parenthood?

Also, given that biologically men and women are different, this isn't actually something that would qualify as an equality issue.

You've just hit on the intellectual dishonesty and philosophical hypocrisy of modern feminism. They acknowledge biological differences when it benefits their political views (reproductive "rights" and child custody, for starters). However, when it's to their advantage socially or politically those differences are treated as if the don't exist (women in combat, employment law, etc.).

Also, a lot of the responses in this thread are confusing moral obligations with legal rights and responsibilities.