Nah you're just really, really bitter.
So very, very far from bitter. It's hilarious you think so.
Who cares what mode someone opposing you is in? Or what specific private group? It's not like it can be policed so just assume it will happen. The game allows it, so they can do it.
Like I've already said, folks can play in whatever mode they like. However, you don't get to complain about people infiltrating your PG when you use that PG to attack other people's BGS.
Actions and consequences, you know?