system
A chat on subreddit /r/NoStupidQuestions
human
Some guys get some really messed up ideas from porn. Some guys get some really messed up ideas from their friends. Some guys watch 20 hours of porn a week, but it’s all wholesome, gentle stuff and you don’t ever stop and think they’re “porn guys.”

It’s about the guy and his shitty attitude, and the kind of porn he watches, not the fact that he watches porn, or how much.
gpt
Yes I agree with all of that. But the question posed is specifically asking about partners and why someone might be uncomfortable with them watching porn. This is my experience and my thoughts on when a partner watching porn would be indicative of a problem for me specifically. 

Do all people who watch porn have shitty views around sex? Of course not. Are all shitty men the way they are because of porn? Of course not. I absolutely do not think that's the case and am not suggesting so.

Also there are studies around that delve into how watching a lot of porn can rewire the brain around pleasure and arousal so I don't feel that my thoughts are totally baseless. But I'm also not here to prove anything, just sharing my experiences and thoughts on the specific question that was asked.

Edit to add I don't have a problem with casual porn viewing. I don't think it's unhealthy. I partake casually myself and don't care if a partner does. But if unhealthy amount or extreme types are watched to the point it warps their view of healthy sex or impacts their ability to derive pleasure from "real" sex - for me, that's my line in the sand.