In all honesty, the core concept of the meme isn't bad, but the way it's was what made it so unbearable. Let me explain:
"NPC" was fundamentally about the idea that there are people who don't really think. They just act as though it's a program in their head. Imagine the simulation hypothesis but instead of you being real and everything else being a simulation, it's everything else that's real and there are individual people who are just simulated. It's also kind of like the simulation hypothesis in the sense there is no earthly way to prove it right or wrong.
Then it got picked up by people who believe themselves to be free or independent, who naturally came to the conclusion "well, I can think, therefore I'm not an NPC". Cogito, ergo sum. And they came to the conclusion that if they aren't NPCs, and they are all unlike a certian group of people (the mainstream), therefore the other group of people must be NPCs, because they all share traits that seperate them from the non-NPCs. And then, they came to the conclusion that if those they oppose are NPCs, then NPCs must just be those who oppose them. Therefore, anyone who thought differently than them were a programmed hivemind. Ironic.
In short, it basically became the inverted version of the "Russian Bots" conspiracy theory.

PS: I'm not trying to generalize 'them' here, I'm just pointing out this one, vaguely defined group of internet users.

I just find dehumanizing people in general objectionable, even as some kind of gag. Reminds me of a couple times in history when some people tried to live by 'theories' that certain groups of people aren't really human beings-- wasn't pretty, they never lived that one down.

And I know what you'll say, that it's satirical and that nobody really believes this, but you'd be surprised. 4chan does that a lot, it's "ironic" until it's not anymore.