Why Is Porn Controversial?

Trying to understand why some people are offended by porn? I see all these "my hubby watches porn and i hate it" posts and I want to know what causes the offense.

I'm not suggesting anything either way, just curious. My SO and I watch porn together as it gets us both in the mood. Sometimes we watch alone when masturbating. I guess it doesn't bother me because i trust my husband, and i know he doesnt watch porn because he desires something else.

Anyway, curious about others' thoughts?