There is a difference. I think you see it to be more than what it is. Pregnancy is not the act of creation; that moment already came and went.
And it took two folks in the back of a Volkswagen or some other more comfortable place (Mallrats reference, snoooooch) to make that happen. From that moment on there was a new human that those two folks should be held responsible for.
Let's try this another way, then.
If the biological father had been involved with the mother, then abandoned her, and then some other man comes along, marries her, accepts that child as his own? That is something else than what happened here.
Perhaps the word "real" is poor a choice for either in those circumstances. There is a father that embraces and accepts a child that knows he is not its biological father, but he takes on the social role and expectations of that man. He is not the biological father, but socially... and yes, I guess in a very real way, he is a father to that child. But the biological father is also a father in a very real way.
If we're being strict about definitions and not including performing the social expectations expected of someone else, then no, such a person can never be a father... but even then, you can modify the term... "adopted father," "stepfather," etc. And we do. This is descriptive. But the biological father does not even truly need the term "biological," now does he? That's implied. Every Homo sapiens has one; we're a sexually reproducing species.
* * *
But in this case? The above never happened. The man never accepted that social role. He never had that opportunity. It was stolen from him. His wife betrayed him. He never, ever consented to raise the children of his wife and another man, and another man, and another man. He is socially nothing and biologically nothing. He was simply a victim. The state is compelling him to continue being his ex-wife's victim. That is wrong.
Gladly, though surely, if we are consistent individuals, and it seems we both are, the same values that inform our positions on that issue will inform our position on this issue.
No, certainly not. But then, they have abdicated that responsibility... in a responsible way, in a way that allowed someone else to voluntarily accept the financial and social obligations of their role, obligations that the parents no doubt felt they could not provide. There is nothing disreputable in that, nothing to disparage, and no, the terms of this arrangement sever financial responsibility.
No, certainly not. See above.
They are not his children, not socially or biologically. He never agreed to adopt the children of three unknown men and his unfaithful wife.
He is financially responsible for his child... and only his child. He created that child.
He never agreed to adopt the other three.
No, not for that... But she does owe him.
How much is 50% of the room and board expenses for three children over the course of over a dozen years? He never had the opportunity to agree to pay for those expenses that he was not liable for. He was the victim of a con, a fraud, and frankly he should be entitled to recompense.