Even if you enjoy porn and you perceive no negative affects on your relationship, it is still negatively affecting someone. The people you are watching sexually arousing themselves and engaged in private acts are someone's daughter, wife, husband, brother and son.

This isn't monogamous behavior. If it doesn't bother your conscious and you are fine with it, would you want and encourage your daughter to join in? What you do mentally does affect your relationship. Your spouse and you are not exclusive in that case.
I also used to watch porn and now choose not. My relationship is far better than any I have had where porn was involved, besides using other people , outside your committed relation, for your sexual gratification is just not something good or beneficial to anyone.

Porn objectifies human beings. If you are fine with that it's just sad.