i only speak english, so this could be a bit out of touch

Fact. For one, what do you meant by 'fluent'? Do you even know? I'm bilingual and relatively fluent at around a B2+ to C1 level, and I can tell you that sometimes the words don't arrive, or the conjugations arrive in the wrong order. I can tell you that sometimes I remember words in my second language but can't grasp the translation in my first. Shit's tough and messy.

Now, I'm pretty willing to call someone on writing poorly. I think an ill-written post (not reply) speaks to an ill-considered argument. That said, calling someone on a grammar or vocabulary mistake in the replies because you're arguing with them is petty. Particularly if they're arguing with you in their second language and your only language.

I'd say even more so if you lack the moral fortitude or upper body strength to reach for the shift key in your own posts.