I don't watch porn. So all guys don't watch it. I've seen it, obviously, and find it so fake it doesn't hugely interest me. Can I watch some and enjoy it, sure! But damn, it's generally shit.
The modern step brother/sister stuff turns my stomach. The Japanese stuff always disturbs me (they are into some shit I don't like).
I may be an anomaly, I don't know. I always liken it to watching the Olympics. If I watch that and assume prospective partners can run 100m in sub 10seconds, I'm fucked.
I have seen porn that does float my boat, but my tastes are not typically the pro stuff.
Porn doesn't have to be a negative thing by default, but it's like anything, if your partner isn't into stuff that (drink/drugs/niche porn) floats your boat, then it isn't the best recipe for a good relationship.