I can't speak for what most think, but I've chatted with a number who view that any money being used to purchase sex is inherently coercing someone to have sex, even if we assume that everyone involved in the transaction is fully consenting. Another view I've commonly heard is that possibly engaging in sex trafficking is wrong (so that all paying of prostitutes is wrong because you can't be sure if they really want to or if they are forced), but that possibly engaging in other forms of human trafficking aren't wrong (basically think of anything you buy at the store which may have been produced by slaves, for a concrete example look at shrimp and the slavery involved with it).

I'm not saying most hold this true, but a sufficient number of my anecdotal experiences lead me to estimate this is a popular view.