"Because the poor rely primarily upon public hospitals for their medical services, denials or delays at those institutions are tantamount to a denial of prompt medical care solely because these women are without funds. A partial explanation for the marked disparity in these figures appears to lie in the far lower incidence of abortions performed for psychiatric reasons among poor and non-white women. While socioeconomic conditions never per se legally warrant therapeutic abortion, socioeconomic status nevertheless frequently determines whether or not an abortion will be performed, and if performed, whether that self-same abortion will be therapeutic or criminal."