No, No Native Dialect Is "Bad English"
Here : "The modern study of language has shown that all native speakers are experts in their language. Almost all judgments about someone's language – the laziness of a glottal stop, the slowness of rural speech, the supposed ugliness of a particular urban accent – have no linguistic justification and reflect only the prejudice of the judger." This is a nearly incontrovertible finding of modern linguistics: no speaker is " grammatically challenged " at speaking their native language. Their grammar may be different than yours, but there is no objective criterion by which it can be judged worse.