I would agree that there's no particular type of person who would have an affair, and any person could potentially have one.
However, I know I will never cheat on DH, as I love, like and respect him - and our DC - too much.
And I say this as someone who has cheated in the past.
With DH, there's just no way I'd ever cheat. I believe he would say the same. Could he cheat on me? Well, yes of course - I can't 100% guarantee he would never cheat, but I live life in the reasonable certainty that he won't. For the same reasons I won't.
Before we got together, his Mum was in hospital having had a heart attack. In the waiting room, with his Dad, his Dad said to him, 'if you ever met anyone half as good as your Mum, hold onto her with both hands and never let her go'. He told me this.
Some people are actually in happy relationships, where it's less fundamentally about love, and much, much more about like. When you like the person you're committed to for life, you don't want to hurt them, and you make your choices based on that.
So no, not all men (people) would cheat, given the chance, or knowing they could get away with it.