Yet even in the avenues of the legal trade there are a multitude of abuses. Underage girls in pornography, extreme fetish videos that border on abuse, human trafficking, and extremes of abuse and drug use are all areas that have been tied to this industry. Prostitution has an already long list of abuses tied to its profession, so merging the two and providing legal protection does seem a poor idea.
I'm sorry, but I don't think that argument holds any water since all fields of human endeavour contain a multitude of abuses. Medicine, charity work, religion, government, orphanages, fire-fighting, retail, police, education, alcohol, banking, music, stock trading, hollywood... These all have substantive histories of significant abuse and those are the ones I can think of with about thirty seconds.
(I'm assuming that the cases involved here are famous enough that examples are not required once the field is pointed out, however if you disagree I am happy to provide examples).
People commit crimes in any field they are engaged within, it's an unfortunate factor of human nature. However, only by banning these fields themselves could you possibly create a situation where the victim of the crime will assist the criminal in keeping their crime secret. (In order to conceal their own crime of providing an illegal service).
As for drugs, the example proposed is one that can show the destructive nature of drugs. People have their lives destroyed by the laws against drug use. Yet the laws are well known, well posted and they can be informed on the repercussions. People still take the risk in order to obtain mushrooms and weed. So obviously they view the destruction of their lives as a fair trade to the temporary boon of the drugs they wish to obtain.
So according to that same argument, television shows have a destructive nature? People have destroyed their lives by downloading TV shows and being charged with piracy offences.
I think you've made the same crucial mistake in both of your arguments. You've taken facts of general human nature (1. We commit crimes, 2. Our judgement is biased towards present versus future consequences of our actions) and then highlighted their occurence within the fields you are arguing against as though they were specific to that field and not universal occurences.