As someone who speaks another language, and has studied several others I always find it humorous when people become super sticklers about grammar.  Don’t get me wrong, grammar is necessary, but I’ve lived in situations where grammar wasn’t as necessary as understanding.  To be picky about grammar sometimes kept some exchange students from speaking up at all for fear of saying something silly.  How are you supposed to learn the correct way to do things unless you go forth without fear of doing something wrong?  
 
Unfortunately I had the gumption to learn German as my main secondary language.  Germans are very proud of their language (as they should be) and thus are very particular about grammar.  Many of their grammar rules make logical sense and German spelling is fairly phonetic, yet despite it’s logic there are plenty of German grammar rules.  So I choose to study a language spoken by a group of people very particular about grammar, with precise logical grammar rules and lots of them.  Suffice it to say, I was corrected a lot.  
 
Now, without those corrections I would never have become a bietter German speaker.  So with this logic, it brings me to this question.  Why do I criticize others for poor grammar online, especially when I don’t know what their native language is?  For many people online it’s not apparent.  In the US especially, where many people come from various different historical backgrounds, you can never know what their native language is.  There are many Americans whose parents speak their home countries native language, but they themselves do not.  Yet, I believe, they are still affected by the exposure to their parents quasi English skills.  Should we judge or criticize their grammar more because of a circumstance they had no power over?  Especially when we really have no way to tell one way or the other?  Not to mention, when they’ve already worked harder to get there than many of us have.

To assume that the person is a native English speaker when they post in English online seems unfair.  If they are not, we are taking in a certain set of criteria when determining their “abilities” and we are judging them on it.  Many will argue, what other option do we have?  Which, when it comes down to that, you’ve found yourself in an argument for or against stereotyping.  Many of the great artists and creators out there had a rule that encouraged idea growth; don’t knock it till you’ve tried it.  Look at many of the great hackers out there, they try not to judge because who knows where the good ideas will come from?  

With this thought in mind I will continue to plow ahead.  I will also try to take my own common sense to heart and do my best not to allow judgment to occur when I see grammar errors.  Just because someone cannot communicate with you on your level in your native language, doesn’t mean they don’t know what they're talking about.