Loved your answer. Feel like keeping it.
We have to pay attention to what we feel. When I found my BF was looking at P I felt bad. I tried to be open minded about it but I felt upset. I did not even want his touch. No matter how I try to rationalize it (and I also get turned on my it when I look at it alone), I felt rejected. I do not watch it with him because I cannnot bear seeing him being turned on by another woman, even in a computer/tv screen. Also, often these women are 20 years younger than me with perfect bodies and faces, which doesn't make me feel that great.
So I avoid it. It's my preference. I respect those who like it and don't mind it. I think it does influence the way you think about relationships. You can start thinking it is ok to have S with that stranger in the metro or an orgy with your best friends. And we all know these things just mess up your mind.