Having played co-op on launch week, I didn’t really see many problems. There was a glitch here or there in act 3, but much less than anyone could expect from a game of this size. I never had to reload any saves, and the game never crashed. The only obvious glitches were certain events happening out of order or not happening when they were supposed to. Apart from that, certain class abilities and features didn’t always work correctly, but every cRPG ever released has had those, and has them to this day.
I imagine it’s about prevention rather than discipline in their eyes. I’m not defending the idea (who cares if we see chun li naked? There is much worse on the internet) but I don’t think blacklisting the player would assuage their fears of it happening in the future.