there are others who are simply bad spellers, or do not exhibit perfect grammar

And this is excusable why?

they feel slighted

This is a different problem -- either the person takes offence easily, in which case they should just get over themselves -- or the person doing the correction wasn't careful enough to avoid offence, in which case they need to be reminded to be more polite.

picking on people

It never comes across to me as 'picking on people'. Maybe I need to be reminded to be more polite?