Not the psuedo-father's concern. Arguing from the child's welfare is like arguing from the fetus's defense if the woman pursues an abortion. It's secondary to the main concern of freedom. You are not obligated to be chained at the hip by deceit. The law is explicitly intended to enact justice, not to care for emotions.
You are equating a fetus to a child, but legally they aren't the same thing. Abortion - from a pro-choice argument - is about bodily security until fetal viability occurs. Not about whether or not a woman should be caring for a dependent human being.
Like I said earlier, if the roles were reversed and a father brought him a child from another woman, should the law force his wife to provide for this child, even in the case of divorce?
From what I understand, a child born into a marriage is presumed under the custody of the couple unless otherwise legally arranged. So yes, if a woman married to a man accepts caring for that child (say the child was dropped off at the doorstep), and it's discovered that the child is the man's biologically from an affair, the wife I think should have certain obligations for the welfare of the child if after 3 years the couple divorces. Most people wish to maintain a bond with a child after helping to raise that child except for a rare few (namely, apparently, you and one of the men cited in the article I linked to above).
I do recognize that abandoning children is not limited to men, and that plenty of women have abandoned them as well. I hold the same opinion of women who cut off all ties to child after establishing that bond as "mom", just because she was wronged by another adult. My point is
the child should not be punished for the wrongdoings of adults.
Another thought......a scenario that might work legally and ethically is that a man can have the choice to ask for a DNA test at birth up to 2 years (before the child is completely cognizant of an attachment to a father figure). If he discovers the child is not his, he is free to divorce himself from legal obligations to the child, but if he denies any DNA testing, and willingly commits himself to raising the child after he or she is 2 years old, then he waives the right to severing support or custodial rights to the child since he has legally assumed the parental role.
Family responsibility doesn't begin and end with bloodline, otherwise we wouldn't see the success of same sex couples raising children, adoptive couples, or stepparents being thought of as "mom" or "dad" to the kids. Human beings have free agency (out of concern for the adults), but they also are not property (out of concern for underage children), and should not be considered worthy of care only if a man sired them.
It's a complex issue that SHOULD consider all adults involved, but 1) it's not comparable to bodily rights as abortion is to women, and 2) it must consider the welfare of the child first.