Telling people an opinion that think X is a terrible game - that X doesn't play like a D&D game - that's not treating anyone badly.
So, this is the fundamental failure of empathy that generated the edition warring dynamic.
If someone says they love a thing, and you look them in the eye and tell them that thing is utter crap - you are treating that person badly. You are treating them as if your opinion of a game is more important than their feelings. To see that clearly, go find a 5 year old child who is happy about the drawing they did. Tell them that it looks like their cat threw up on the paper. Watch what happens. Adults have filters, a somewhat thicker skin, and some coping techniques, but the emotional core doesn't change.
Even further, if you tell them that the D&D game is not D&D*, you're closer to being the southern end of a northbound horse.
Humans are tribal animals. Being a gamer, being a fan of D&D dedicated enough to discuss it on the internet, is part of the player's identity. In saying, "Your game is not D&D" you are, by extension, saying that person isn't a D&D fan. You are rejecting their identity as a fellow fan. You are casting them into the out-group.
If you don't realize how it is hurtful to do that, the problem is not the game. The problem is that you are so committed to your opinion that you have failed to think about the other person in the discussion. It is common on the internet to forget that the person you are discussing matters with has feelings, but that doesn't make it okay.
If you do realize how that this hurtful (as many at the time did), and you do it anyway, you are being a schmuck.
The typical statement was *not, "X does not play like a D&D game". It was "X is not D&D." Softening it is revisionist history.