"Although contraceptive services are legally available in all states to married persons and in almost all states without regard to marital status, in fact contraceptives are not readily available to a substantial portion of the population. This is particularly true of urban and rural poor in many areas of the country. In some of these areas even non-prescription and relatively ineffective contraceptives cannot be obtained. Even if some form of contraception is available there is likelihood of unwanted pregnancy since the most effective and practical contraceptives, such as the birth control pill, the intrauterine device, and the diaphragm can be obtained only on the prescription of a doctor whose services are denied to hundreds of thousands of poor...."