To me this comes down to something very fundamental: no one should have to bear the consequences of a decision they are not responsible for. this hinges upon believing that pregnancy is no longer a natural conclusion of sex. I think that's a safe position to hold because of birth control.
by allowing women complete control over whether the baby is born and requiring something of men if she makes one of the choices, we are creating an unfair system. any freedom women have because of this comes at the cost of a man's freedom. true freedom for a woman should include only her freedom to make decisions that will affect her. that should include associating with people who are likely to stick around and raise the baby if that's what she wants.