What I said was "states COULD make only married fathers be liable". Some states (e.g. Texas) did so. Other states made the biological father liable regardless. What the Supreme Court decision did was to forbid states from making illegitimate children ineligible for child support.
My poor reading comprehension is to blame (though perhaps you could have also worded your original statement more clearly).
It used to be (before a 1972 Supreme Court decision) that states could make only married fathers be liable for child support.
The casual reader (and I admit that, in this case, I was one) can easily infer that, prior to 1972, only fathers married to the mothers of their children were liable for child support. I can see now that, instead, previous to 1972, individual States were free to exclude unmarried men (or men not married to the women of the children in question) from paternity suits; and that the 1972 Supreme Court ruling then prohibited such an exclusion.
Thanks for clarifying!
Regards,