Everybody speaks in a dialect.
Speaking without a dialect is like typing without a font. The only difference is different dialects have different amounts of prestige. In the UK, the prestige dialect is RP. It's perceived as posher, more refined, more sophisticated and its speakers are thought to be more intelligent etc.
This isn't because of anything inherent to the dialect itself, it's because of history. That way of speaking is how the people with the most power spoke back in the day (again, massively oversimplifying). If those people had been based in northeastern England, then Geordie would've become the prestige dialect.
There's no scientific basis for calling any way of speaking superior or inferior to any other, any more than there's a basis for calling one species of animal superior or inferior. Don't believe me, have a look at the situation in Switzerland, more specifically the German speaking part.
There, everybody's native language is their local dialect. That's what they speak to their parents, friends, bank tellers, shopkeepers, barbers etc. It's what they speak in professional environments, job interviews, sales pitches, business meetings.
But in school, they're taught to speak Standard German. That's what they write down, it's what their newspapers, websites and governmental communications are written in. This means all German-speaking Swiss people essentially grow up bilingual in their local dialect and Standard German
Does this mean Standard German is inherently superior? Say that to a Swiss person and you'll be swallowing your own teeth
No, they just use it to communicate with Germans and Austrians, to whom their dialects are incomprehensible. But they're not incomprehensible inside Switzerland, their society gets on just fine by using them internally.