[betterunix]

"Something that just came up to me: why is making porn movies for money legal, but prostitution is illegal?"

The law is not a strictly logical system (this is usually a good thing, despite the common negative perceptions). Pornography was once illegal; then the interpretation of the law changed so that it would be considered "protected speech," unless it is being displayed in certain contexts. Prostitution is illegal in most of the USA, except for certain forms which are not illegal (e.g. it may not be illegal to have sex with your boss in exchange for a promotion).