What is the reaction of linguists to the claim that sentences of this sort are wrong?

He don't know about the race - According to the dialect the use of 'don't' is acceptable when there is a singular subject. You was out when I called - According to the dialect the use of 'was' is correct when "you" is the subject. There is twenty horses registered in the show - According to the dialect the use of "is" with "there" is correct.