Child support payments are justice because the children need to be financially supported for food, clothing, and the necessities of growing healthy (medical care, etc.). Whether or not the man would like to fancy himself responsible enough for the proper care of his offspring, the court and social services determine who gets custody of the children based on things like...the man's attitude toward responsibility and such. If the man is the type of person who resents the responsibility of paying child support, or thinks of women as sluts, or uses language that degrades people and feels free to always say that women go "a-whoring", then social services makes the correct judgement that the man is not fit to properly care for the children (I thank God that they make these decisions and give custody of the children to the most responsible of the two parents).
As to the PAYMENTS of child support, whether the mother has a million dollars in the bank or not (unlikely of young mothers), the father should not begrudge the children or MOTHER (not "slut", on Mother's Day, we celebrate MOTHERS, not "sluts") these payments. There are fathers who do resent making these payments (and I am glad the law is on their case) and still put money in the collection basket to give to the needy (The Lord knows they do it GRUDGINGLY and self-righteously, The Lord loves a cheerful giver). They are fooling themselves into thinking that they are growing closer to The Lord or will ever have the ability to grow closer until they stop begrudging ALL GIVING, but they will also have to learn not to RESENT being accountable (held responsible) for their actions whether their actions be intentional or careless mishaps. In the bible, The Lord informs us of the right way to do things. Because it is "human nature" to RESENT being TOLD (The Lord is not holding a gun to our head, we are being INFORMED) to do things the right way, we become obsessed with everything He says as being a COMMAND (because to some people, it MUST be) and end up caring very little about His "WANTS" and His likes and dislikes. He informs us of the right way to do things because He WANTS us to live happily and have joy in life (but apparently few of us really care about that because it's not a command).
Your friend should put his resentment and irresponsibility in check.