Matty, if comment was restricted to those who are informed and knowledgable there might not be very many comments ;)
And who is going to decide whether a comment meets your criteria? I presume people who post remarks are not sitting thinking "I'm ill-informed, so I'll expose my ignorance by making a stupid comment."
I know this will astonish you, but even I have been known to say things which show an astonishing lack of erudition. Fortunately, that allows people to correct me so I know better next time.
The moral of this is that you shouldn't ban people you don't agree with, you should point out their mistakes.
I'm sorry to hear about Sheffield. It sounds as if the education system is failing to get the right message across.

How do you "earn a British passport"? I never did anything to get mine. True, I had a great-uncle who was killed in World War I two days before my mother was born; and my uncle was wounded on D-Day with the Paras as the glider he commanded landed behind enemy lines. But I didn't do either of those things. Perhaps I should hand it back until I can think of something I did to "earn" it.

If you were addressing your comment about the likelihoot of a Sharia take-over of the UK to me, I don't believe for a moment that it will happen - at least, not within the next 100 years.