It depends. Some groups are shit. Some aren’t.
Some people have genuinely positive experiences with polyamory. And many polyamorous people feel pressured to always be good PR because of how often people assume that polyamory is a reason a relationship failed and not the people involved.
But, I’d say that’s true for ANY group you join. If you joined a DnD group, I doubt they’d start off by telling you all of the shitty DnD games they’ve played, yeah? I don’t think polyamory is unique in that regard.
The important thing is to have a community you can talk to and hear different experiences rather than just mainstream mono-centric society which will immediately assume open relationships are ‘impossible’.