Male and female human beings evolved with stark biological differences in organs, hormones, bone structure, musculature, brains, auditory and optical awareness and instincts that make it impossible for the law to create equality in every aspect of life. Women are biologically excluded from playing in the NFL, NBA, NHL, etc. Men are biologically excluded from abortion
Arguing about the fait accompli of evolutionary biology is a bit silly. Have the differences been used to inappropriately exclude both male and female from areas of endeavor. Yes, examples abound. However opting out of child support because women can abort a fetus is not one of them.
Legal terminology like "equality under the law" does not change from situation to situation or person to person.
Women have opted out of responsibility by getting an abortion which is the death of a fetus and an end of all responsibility for everyone and every institution forever for that potential child. Equality for men under the law then means the same thing; an end to all responsibility for everyone and every institution.
Only by redefining "equality under the law" to mean men can choose or not choose to accept responsibility for his child can the father opt out of child support. The mother, family, relatives, insurance companies, hospitals, vital statistics bureaus, city services, churches, schools and the state still bear responsibility for the child. That is not equality.
Until we establish a theocratic police state in which men can legally require women to abort a fetus men, along with everybody else, have to support the child he fathered.
You can't change either biology or legal terminology.