Everybody, which knowledge threw me for a very unfortunate loop after I quit. There is no way that a "hobbyist" looks. Most of them were between fifty and seventy years old, vaguely conservative, well-dressed men. But I also had clients in their twenties and a client who was younger than me. That, I think, is the scary part, that as the older generation of men who would pay to abuse a woman heads towards an impotent sunset surrounded by nurses who would most likely not call in an escort upon request, more and younger men rise to take their place. This is not a problem that is going away. This is not a problem that can be ignored.
I'm not saying it's an immutable fact of male nature, more that our society is training young men to hate women just as surely as it trained their fathers. Only the younger ones can rationalize it better.
The thing about hobbyists is that although almost every single thing that a hobbyist does indicates that he associates satisfying sex with hurting women and fails to think of women as real people, they don't really stand out in a society that encourages all men to think about their sexuality in the same terms.
Certainly, it is considered "normal" for a man to watch some violently-themed porn and to occasionally see strippers, and most women I know would only raise objections if they knew a man who was doing it "too much." This misses the fact that when your average man pays any sex worker, he is paying to degrade and sexualize her. The men who do this less frequently are not "okay;" they just objectify women less.