They are not being pedantic here, they are establishing a meaningful difference in words to help distinguish a shared phenomena. I think the original comment was unnecessary and certainly bigoted, but I would need more to say racism. The "grammar" guy clarified twice the semantic difference they personally observed (note they did not labor on syntax like you wish to suggest).

All that said, I make this comment as I believe the other commenter's worry is on display im this comment here...

> Again you seem more concerned with grammar than, y'know, condemning racism, prejudice, or bigotry. They're all equally bad and closely related concepts

These are _not_ all equally bad. Prejudice is foundational to understanding, there is no escape from this. In this understanding, we should treat particular postures of prejudice more serious than collapsing any "bad prejudice" under the same label.

> I think the original comment was unnecessary and certainly bigoted, but I would need more to say racism

Do you think racism is worse than bigotry? Why? I understand that the first word has a more emotional charge in our times. But as far as "bad things to do" go they're equal in gravity. Racism is just a subset of bigotry.

> These are _not_ all equally bad

Why not?

> Prejudice is foundational to understanding

That's one definition of the word - "judging without knowing the facts".

But there's another definition - "an irrational hostile attitude, fear, or hatred towards a particular group, race, or religion" - which was the one we are operating with in this thread.

https://en.wiktionary.org/wiki/prejudice#English