Absolutely, the law should have no say over matters of morality. As far as spreading STDs -- in developed countries where it's legal, the opposite has been true. Legalizing it requires that practitioners acquire proper licensing and health certifications, and they have to have those health certifications renewed on a monthly basis. Health benefits for those who get pregnant as a result of work are outstanding, including maternity leave with full pay, and all prenatal and delivery expenses paid for those who choose to keep the baby.
Does anyone really think that making it illegal has slowed it down? It just means that those who go out and pick up a hooker have no idea who they actually are, no idea of their health status, and they generally have the freedom to take them anywhere they want -- which is extremely risky for the professional, as is so often proven when they're found dead in back alleys or dumpsters. Legalization allows for a set place of work, and security that would greatly reduce the risk of bodily harm for those in the profession.
And yes, taxing too.