As noted, there are many reasons why someone might have a problem with spelling or grammar, such as ESL or low IQ.
Could be he/she may have suffered a brain injury?
I find it strange that if someone had a Limp or other physical disability, we as a society, would likely consider it 'Bad Taste' to make an example of, or point out "Hey, look at this guy, he can hardly walk. What a looser!"
But if some poor soul has poor grammar, they are often considered Fare Game.