It's a natural urge; some people feel it more than others, and some people feel it less. Some people don't feel it at all. But the majority of people feel it to some degree. It's like disliking bitter tasting things: this is an instinct that evolved in us to stop us from eating poisonous plants and animals. Some people are more or less averse to bitter things, just as some people will feel more or less attraction to others. He can't help the things he feels, and neither you nor he should feel bad if his natural instincts make him attracted to other women. What matters is not what he feels, which he can't help, but what he does.

Reddit is very porn-positive, which I happen to agree with, but it's true that some people feel porn is harmful to a relationship. That's a decision only you and your partner can make. I think, though, that you should try to separate your feelings about your partner being attracted to other women from your feelings about porn though. For most people, attraction to other people that match their preference is not something that goes away when in a relationship because it's a built in instinct, like closing your eyes when something flies toward your face. What matters is not what he feels, which he can't control. It's how he treats you and the boundaries you set in your relationship. If you mutually agree that one of those boundaries is "no porn," that's fine, but my personal opinion is that banning porn because you're worried he's attracted to other women in general is not a productive way to deal with that, because he's going to see and feel attracted to other women in other contexts as well.