Judging People by How They Speak…?

I’m from central Scotland and we do speak fast, but we’re not alone in that.
It is irksome to be constantly told to slowdown. We have had to learn to adapt, for instance, to the constant estuarine English which is barely intelligible to us. I gave up on eastenders years ago.
Your right it’s nothing to do with intelligence but it is about common humanity. If you are interested you will put the effort in and understand.

Where I come from we are made fun of, think of the Catherine Tate sketch where Jill Halfpenny is the new nanny and they can't understand a word she says.

No it isn't on Fanny and is bigotry. As Katie has posted, some regional accents are difficult to understand but that's not an indication of the speakers lack of intelligence.

There are many accents the problems are caused by not being understood, I work with a Glaswegian colleague, she speaks so fast I just have to say slow down, every time, if she only thought first it would be fine.

www.thetimes.co.uk/article/brummie-accents-rated-least-intelligent-rcmz3bxlnhl