why do some women make a big deal out of porn?

Jessica
Why do some women get so upset by their man watching porn? I just can't understand it. It's not real sex, they're just watching it. What about sex scenes in a movie? Is that not allowed either? And 50 shades of gray is that not okay for you to watch or...? Please explain, so I can understand.
UPDATE: first of all, I'd just like to say that for those of you assuming my marriage is on the rocks or something your %110 wrong. I love my husband and he loves me and I don't even know if he watches porn because I've never asked but I don't care if he does. I feel secure in my relationship, and don't question that he loves me. The reason I asked this question is because I wanted to understand the reasoning behind it. If you're thinking I don't need to know the reason then that's fine, just kept it to yourself but if you'd like to share, I'll listen. Thank you all for your input and view points, I have to say that I never took porn so seriously before and it's good to look at both sides when it comes to issues such as this.