I'll challenge you right back in the same spirit. You suggest that we might be alienating people who could enrich the world of poly by excluding cheaters (cheating meaning breaking the rules, whatever ones you and yor partner or partners set for yourselves, whether examined or by default). But what value or enrichment could people who are lying bring to the community?
They can't help us figure out how to have respectful relationships with your metamours, because the metamours don't know about each other. They can't enter the conversation about how people deal with jealousy because they're attempting to skirt the issue of jealousy entirely. They can't speak to the process of coming out, or co-habiting with multiple partners, or when to introduce a new partner to the kids, or rules negotiations with your partners.
I would say that cheaters don't have a valuable role in the poly community because, aside from loving more than one person, which we already know how to do, they don't deal with any of the same issues, questions, or practicalities.
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.