Porn is far more acting-based, whereas prostitution is entirely pleasure-based. They both have to look the part, they both have to have appeal, and they're both selling their bodies, although prostitutes sell their bodies directly while porn stars sell images and videos of their bodies more than anything else. I think that as vocations they're quite different.

And I disagree with the legality of either of them solely because I disagree with the morality of either of them, but that's just me. I can live with either being legal because I personally am not interested enough to be a partaker of the fruits of either industry anyway.