It's a sorry state of affairs if television should be completely responsible for educating children about understanding and tolerance of other cultures. That's where one may be forced to do some parenting. Sorry to break it to you...
Oh and by the way... I'm unlucky enough to live in an are without many ethnic minorities, I'm sorry to say that I've never even met a Rastafarian. It's odd then that I should be able to understand every word spoken on the programme, despite the heavy accents. That's why I don't really buy that others can't.
Mind you, I shouldn't be so harsh on you lesser mortals. It might all be down to my awesomely high intelligence, not to mention my startling good looks. ;)