Cheating just to cheat is disgusting to me. It's an actual fetish - I've actually been approached by guys and when I said I'm in a relationnship, been told "That's ok, it's kind of hot to be the other guy". So that's gross to me. And I don't condone cheating. But... life is complicated. Every situation isn't a simple "if you're not happy, leave" situation. They might not be able to leave because of money. Or abuse. Or because their partner is sick or one of their family is sick or going through another kind of hard time, and they don't want to desert them at that time, even though they're not happy. Or, one of the scenarios where I think it's totally ok to cheat, is your partner has a debilitating, and or terminal illness, that renders them less than conscious. Maybe they have alzheimers. Maybe they're in a coma. They've been in that state for years and it ain't gonna change. You don't want to divorce/break up because you love them and you meant it when you said you'd always be there.. but at the same time, you still need love and affection. So you find someone to spend time with... to have sex with, talk to, ect. There is no way your partner can find out because they're non compis mentis (I love Bugs Bunny). So who are you hurting? You're getting support so you can go home and explain to your alzheimers-ridden partner for the thousandth time "I'm your husband, sweetie".
So no.. cheating isn't always wrong.