The issue has nothing to do with what two consenting adults are doing. The issue is how pornography affects society's perception of women. If pornography promotes violence against women (something some people claim and have studies to support), then what those two consenting adults do on film very much affects ALL women.
It doesn't matter what third parties think about interactions between two consenting adults.
It sure as shit does when it potentially increases rape and battery rates, affects workplace treatment, general social treatment, societal perception, etc.
Personally, I think pornography is wrong and degrading to women
But women also watch porn. Why would they watch something that's degrading to them?
Because "women" are a diverse group that do not all share the same opinions on everything, believe it or not. Some like it, others do not. Some like certain porn while they dislike other types of porn. The world is not black and white, try hard to understand that.