Wait, I don’t get it. Are you saying making a grammar mistake makes someone a shitty person? And not correcting grammar enables people’s bad behavior? Like being ungrammatical is morally wrong or something?

And let me Google the def of pretentious real quick:

attempting to impress by affecting greater importance, talent, culture, etc., than is actually possessed.

Correcting someone’s grammar online is absolutely a pretentious act. You’ve identified a grammatical mistake - which in this case isn’t even a mistake but a difference in dialect - and you feel the need to call them out on it? What possible benefit does that have except to show off your allegedly superior grammar and thus demonstrate your superior intellect, talent, culture, or whatever aspect of life you think grammar should be assigned to?