When you got married, you promised to honour your wife with your body; watching porn is doing the opposite. You promised to love and to cherish her, and that's what she expects. Watching porn is telling her you don't love her, she's not enough for you etc. Telling her she just has to accept it, that it's normal etc is putting her in the wrong - she's supposed to be your equal and your soulmate, not some second-rate bit of stuff who's good for doing the housework, and a bit of sex when there's nothing else available or because it's your duty. If there are deeper issues, you need to talk, and if things aren't resolved that way, see a counsellor.
Remember, it's not just your wife you're downgrading, it's also the people in the films you're watching.
Come on, your wife is worth more than that, and so are the people you are watching.