It's not a double negative, just a (technical) misuse of the third-person plural. Believe it or not, refined English-speakers once used it this way, and it was considered correct. They also said "ain't," and the King of England "et" his dinner every night. Everybody speaks a dialect. Whether one dialect is better than another is subjective, and it changes with the times. Want to hear something close to Shakespearean English? Visit the Blue Ridge Mountains.