[Faceman]

joining in late again (must be the time difference)
and trying to have an opinion on all the topics

Most important things first.

I think prostitution should be legal (here in Austria it is) because thus it can be better controlled. Some comedian once said that prostitution was "a victimless crime". Well not really but it can be if it is legalized.
1. The John risks getting STDs (don't say he knows the risks drug addictsdo too)
2. The John risks being blackmailed
3. The prostitute also risks her health (but may have no other job oppurtunity so it is either die on HIV or die on TBC)
4. The prostitute may be in a slave-position to her pimp being denied basic human rights

IF prostitution was legalized the health risk could be reduced by regular screenings (as it is done here and probably on other countries with legal prostitution) and the blackmail risk while still being applicable on a personal ("I tell you wife") or public ("the mayor went to a brothel") base would no longer bear the criminal aspect (i.e. you can't be jailed for it).
The slave-position of the prostitute can be bettered but not solved because you're basically in a slave-position in every minimum-wage job.
With existing legal prostitution illegal prostitution (no health screenings, no green card, no taxes) won't stop but it gets unpopular with the legal side of the business and thus is seriously reduced.

Now while most logical aspect speak FOR a legalization the question wheter or not it should be done is a moral one which I do not dare to answer.