One of my main objections to poor spelling and/or grammar is that it really interferes with my understanding of what is being said, or what is trying to be said.

I seem to have an instinct for when something is misspelled, but that doesn't mean I always know what the correct spelling is. I have to look that up sometimes.

Here's another one I see: no = know. It seems people cannot tell the difference if it sounds the same.