As a poly person, nonmonagamy must be consensual for all partners involved. Having sex with someone you know to be in a committed, monogamous relationship is immoral. At best, you are willfully facilitating someone else's victimization. We should not force nonmonagamy on others just as we wouldn't want monagamy forced on us. Obviously, the cheating partner is far more in the wrong, but you're wrong too.

Think of it this way, if you have a boundary in any relationship, romantic or otherwise, and someone else is aware of that boundary but helps break it, they're a shitty person for that. Just because we are wired for polyamory does not mean everyone is, and forcing it onto others and calling it "breaking their chains" is gross. This behavior could easily ruin lives and break apart families, and trying to take the moral high ground when forcing your beliefs onto others and victimizing them is frankly ridiculous. Nonmonagamy must be ethical and consensual, or we're just perpetuating stereotypes and harming the chance of future acceptance.

I hope you're just the manosphere troll you come across as, and not someone that genuinely believes these things. You hurt other poly people and monagamous people alike with these behaviors.