The guy you knew should be forced to pay because he didn't opt out soon enough. If he wanted out, he should have done so while abortion was still an option.I knew a guy though some friends who got his GF pregnant. She had the child. They tried to stay together for a while, they broke up after a year. He seemed like he just wanted to totally walk away from everything. I can understand walking away from your romantic involvement with her, but look, you have a kid. Fine you hate the mom's guts, deal with it, act like an adult. I just couldn't understand what he was thinking. The way I saw it, he was in the unique position, better than any other person out there (perhaps aside from the mother) to make a serious, real impact in this child's life. His support (or lack there-of) would create a dramatic impact.
Nobody is forcing you to have sex. Personally, I've tended to screen who I'm having sex with. Do you want a child? If you got pregnant, would you have an abortion? I've also engaged in some risky sexual behavior, and have had girls tell me they were on birth control when they apparently were not. There would always be the chance that if pregnancy did happen she'd change her mind. Fair or not. An agreement should be an agreement, but that's not how things always turn out. Nobody forced me to have sex with her. But if there was a false agreement, that means I was led into my actions under false pretense.
If there was a real contract in play (technically an oral contract is a real contract, at least it is in business law, but enforcement is something else...), then if no party was under duress at time of agreement than I think it should be binding. Leave it up to individuals to decide if they like the contract or don't.
At the least *I* think you should pay for the child's needs based on what you can afford. Personally, even though at this stage in my life I don't know if I'd make for a good father (really, can any sane person really say "I'm ready to raise control and take full responsibility for another human"), I'd try anyway. It would probably mean a giant sacrifice in a lot of ways, but I'd still view it as my responsibility. It's easier to say that just sitting here than in real life, I'm sure. To some extent, even if the mother and I ended up not getting along I'd view it as my responsiblity certainly not to care for her in the sense I would a child, but to provide support for her. "Are you well?" "Are you stable?"