I think that it is because so much of porn these days is airbrushed, and some women do not realize that.

So when there partner watches porn they feel insecure about themselves as the people on the porn videos are sexy, adventurous. Some women that I know do not feel comfortable performing certain acts with there partner and when there partner goes to watch porn I have found in my own experience that males usually watch the porn relating to what there not getting at home, or in the bedroom. Now I am not saying that this is all men or even women as a matter of fact, but from what I have seen this plays a big part in why people feel insecure about there partners watching it.

A very good friend of mine will not and refuses to try anal for her own reasons, she does not mind it if her partner watches porn but she absolutely hates it when he watches porn that includes anal, because it does make her feel insecure.

I hope that I have made sense