It most certainly is a valid question, but personally I think it is a bad idea.
For a start the current limit is too low - 70mph was the limit set when we were driving around on rubbish rubber and drum brakes: cars are now so much more safer than they once were: some people will nasally whine that that may be so, but it doesn't make drivers better than they were many years ago: possibly, but I think not, as people naturally adapt to their surroundings.
People, by and large, know how to drive sensibly: should we punish those perfectly safe drivers who regularly, and safely, drive at 80mph on a motorway by electronically limiting their cars just because of a few idiots? Seems unfair to me.
Restricting everybody to the same limit is what happens now - break the limit and you are breaking the law - and there are sanctions in place should this happen. Therefore, is it really necessary to go a step further and electronically govern the speed of cars? I personally don't think so - this would be nannyning gone mad.
Joko believes people speed because they think its 'cool'. I don't think she could be further from the truth - in the vast majority of cases people speed because speed is fun: otherwise why would people go on rollercoasters. They certainly don't do so to demonstrate coolness.
Jake says "I'm surprised you haven't been told that it's not speed but bad driving that kills". He obviously thinks this is a trite comment - but it doesn't take away from the fact that ultimately it is, to a large degree, true.