I get that they're trying to distance their fandom from problem behavior, but the definition of a fan is enjoying the group/music and possibly (but not even necessarily) supporting monetarily. A lot of badly behaved fans DO like the group and DO spend large amounts of money on merch/fansigns/concert tickets. Saying that a wave of bad behavior within a fandom "isn't real Army/NCTzens/Blinks/Onces" or literally any other fandom doesn't stop the person in question from cavorting around online and making the fandom look shitty, all it does is make you look like an ostrich with your head in the sand.

Secondly, if another fandom is calling out bad behavior within yours, saying "that's not an (x)" is literally just starting unneeded and unproductive arguments. Like, assuming I'm a member of fandom A, and I say that "the members of fandom B who are sending hate to A are inexcusable", you are adding nothing to the convo by popping in with "that's not a REAL B!" I feel like it's so much more helpful to acknowledge the harmful behavior and speak out against it than to just disown and ignore it. This is the way that bad behavior is going to be shamed and stopped. It doesn't take big confrontation with individuals, sometimes what it takes is people being brave enough to say "I'm a B and it's saddening me to see what other B are saying about A...that's not what either of these groups would want to see they're literally friends" BECAUSE THAT IS SO OFTEN THE CASE.

To make a real world comparison - have you ever complained about a traumatizing experience with men in front of a man and had him start hemming and hawing and saying things like "real men don't do that!" or "not all men are bad people!". Isn't it frustrating? Now imagine instead if you vented about a traumatizing experience and the man replied with "that's fucked up, I'm sorry that happened to you, no one should have to deal with that treatment". It shows solidarity and growth, not offloading the problem onto someone else and turning your head the other way.