It's not so much what your looking at that's the problem, it's the behaviour.

For instance if you seen a hot woman on tv and thought to your self oh god I'd love to f*ck her, that's completely fine. But if you deliberately start searching for any form of porn/artificial sexual stimulation for an erotic buzz then this is actually the problem.

It's the seeking behaviour that's the problem. If you randomly see a hot image/video of a hot woman and think it's hot then that's fine. If you deliberately search stuff like that for an erotic buzz then that is not fine.