You say you're concerned about perception and trying to help him. Honestly, do you think people perceive someone who makes a typo worse or the person who is repeatedly correcting them on an internet forum worse?
It's not a typo, it's a repeated grammatical error. I perceive someone repeatedly correcting someone else's errors as probably having too much time on their hands. I perceive someone repeatedly making grade-school level errors (as covered elsewhere, this is not a common ESL error) as not worth my time to even read. Up to you which of those is worse.
Was wondering if anyone would correct me for calling it a typo instead of a grammar error since if I wrote "your" instead of "you're" it would have been too obvious. Seriously though, I used to judge people the same way right after undergrad. I was young and thought people who made such errors were stupid. But, over the years I encountered some very successful people that could barely write and had to reflect a bit. "How is guy is a self-made multimillionaire when he can barely write?" I realized that my dismissing of people like that made me feel superior but it wasn't actually a good filter. Obviously you've reached a different conclusion by deciding that people who make grammar errors on internet forums aren't worth your time, so to each his own.
There are enough independent correlates of success that any given successful person will almost certainly be missing one of them, if not several. Writing well is one example. That said, it does still correlate to success, and therefore still functions as evidence. There are too many comments on the internet to act as though every one is equally worth reading. It makes more sense to do a quick Bayesian update on the available evidence and move on to a comment that is more likely to be valuable. This isn't a value judgment about the person who made the comment, it's just pragmatism.
Oh, I misinterpreted what you meant then. Regardless, your logic is sound and has lead me to think about things I hadn't considered. So, from now on I won't disregard grammar errors but will instead use them as evidence. That said, I'm kind of stuck on how to proceed when the ideas in a comment are trending towards valuable but I reach a grammar error. Maybe how to handle those is just a function of personal preference or available time? Also, based on your experience, should I consider user names as part of the available evidence?
They're weak evidence. If the first half of a comment is valuable it's probably worth reading the rest. And yes, username is strong evidence. I read every comment I see from patio11, for example.