If you start mainly thinking of women in sexual terms or start primarily thinking of women as a means of sexual gratification, you should probably take a step back from porn. Also, if you start harboring resentment against women who aren't interested in you (or women in general), or you start thinking of sex mainly as something that women use to control men, then you should probably take a step back from porn. Thoughts like these are rather toxic and will set you down the path to creep-dom if left unchecked.
Note: I'm not saying this because I think porn causes these kinds of thoughts or anything. What I am saying is that harboring thoughts like the ones listed above is a sign that you have some unresolved baggage when it comes to both sex and women, and that if you opt to continue consuming erotic media without working on that baggage you run the risk of reinforcing it instead (And that will lead you down the path to creep-dom).
TL;DR: Media doesn't really cause destructive thoughts or behaviors, but it certainly can exacerbate destructive thoughts or behaviors you already have.