That ignorance is bearing some fruit already. Some time ago I saw an interview with a company spokesperson. This person said that the company want some trainees for an office job really badly but none of the applicants could master basic math, basic spelling and basic grammar. So none of of about 300 applicants was fit to even start the training let alone complete it successfully.
Ironically the common availability of spellcheckers seems to promote errors in grammar and spelling.
The bad spelling and grammar also affects the efficiency of communication. Sometimes it changes the meaning of a sentence. If you are lucky the new meaning does not make sense and you have figure out the real meaning. If you are less lucky someone will suffer from the consequences of a misunderstanding.

Disclaimer:
I am not a native English speaker, so please bear with me if you find some errors and feel free to point them out.