“not exploiting students for sex” is one of the most important qualifications for a teacher/prof.
Teachers have a responsibility to their students. They are in a privileged situation, and they can screw up a student’s life if they decide to act on their fantasy.
If a prof isn’t responsible enough to stop himself from viewing porn that exploits students on the computer he uses to teach students, he’s throwing up warnings.
I don’t there is anything inherently exploitative about porn, regardless of the theme. The idea that you shouldn’t be able to explore fantasies because of your profession is absurd. If the issue is with the choice of laptop, sure, but that’s a pretty minor issue, not a huge red flag.