I don't think this is the case for every man at all. Some, maybe.
I came home one night, we were having a small party and it was just me, my friend, DH, and newer friend left. Kids were in my sister's. I popped out to the next village (taxi) for more booze with my friend. Left DH alone with a newer female friend. Absolutely gorgeous, tall, model-like (I'm 5' nothing and while I'm good looking, I'm not a model), properly beautiful.
I came back and no one heard, the doors were closed and lights off. They were down the other end of the garden and you can't hear from there. Was putting the wine out in the kitchen and looked out the window into the garden where we'd been sitting. This woman made a move on DH. He literally swerved back, held her wrists and pushed her back off him. Stood up, yelled at her for trying to cross boundaries and stormed inside. He didn't know I was there, he saw me and panicked in case I got the wrong impression. I saw the whole thing and our security camera proved nothing else had happened.
He was as mortified as I'd have been if a male friend had done that. So no, I don't think all men will cheat if given the opportunity. I know it sounds naive, and I've met the kind of man who would. I don't think I'm married to one of them at all.