The answer to this seem obvious to me, but maybe I'm missing something. What are your thoughts?
In a world in which all women had easy, affordable access to birth control, and women could easily access abortion without restrictions, I would be inclined to say that men should be able to opt out - assuming that they did so early.
This is not the world we live in. If men wish for this to be the world we live in, they are welcome to join the fight.
If the man doesn't want the child but the woman insists on having it, then yes, the fathers obligation should be much reduced (90%?). The father still has some responsibility for not using birth control. The woman may have simply used the man to get impregnated.
Mothers have critical social responsibilities that when violated, deserve severe consequences.