That's classical: The bad speller either has no doubt or doesn't care.   The person with bad grammar has no doubt or doesn't care.

Or a third possibility for either bad spelling or bad grammar is that the mistakes were deliberately taught that way because the teacher had no doubt or didn't care. So the current "offender" defends by saying, "I was always taught that . . ." Or (s)he even "corrects" the usage of others on the basis of correct memory of incorrect teaching, taken as gospel truth.

Dave Oesterreich