What do u think the effects of non-standard accent of English on non native speakers and native speakers of English?

Hi guys.. I'm doing a research on this topic.I define standard accent as any accented English as spoken and understood by the majority of educated native speakers like British accent and American accent. While non standard accent of English is any accent that is spoken by non native speakers. As I know most English learners don't speak like Americans or British. Since accent has something to do with pronunciation and intonation, it must have its effects on people's perception and attitude.

Please give me your opinion about that..