I think it depends what they’re actually looking at, to be honest. Some of it (well as lot) is very disturbing. When I found out my husband was watching porn, I was very upset because I went on the (free) sites he was watching myself to have a look. So much is about rape and humiliation of women and as a survivor of sexual abuse, I found some of it very triggering and ended up in therapy.
However, I now realise I just have to accept that he watches it and I think all
men do to some extent. You can’t control where men’s minds want to go, even though I think porn is very damaging on a societal level. He claims he watches only girl on girl / supposed lesbian orgy type stuff 
. I’ve watched it with him a fair number of times, at his request. I’m not bothered at all about him looking at other women’s bodies as I think this is natural for all men and fortunately, I’m not insecure about my own body. I think men are more visually-stimulated than women and if they just need imagery to masturbate, then I’m fine with that. If he wasn’t watching porn, what would he be thinking about? Although it seems to me that all porn is about degrading women, would not be fine if he was watching anything violent or particularly degrading, or if it affected our sex life or his attitude towards me.
There is, of course, the wider issue that you can never know how many of the women in porn have been abused or trafficked at some point. Men choose not to think about this in any depth because it doesn’t suit them to do so.
What seems most bizarre to me, is that such sites would not be tolerated for any other demographic group. The captions for these sites and the content to many videos is about dehumanising women - replace that with a similar access to racist, homophobic or religious hatred and the sites would be banned in two-seconds flat. Yet because it’s only women, apparently it’s ok.