I don't agree. I think we pay enough tax on things as it is. Everyone knows that too much sugar makes you fat and they also know chocolate bars and fizzy drinks are full of them. Educating people that everything is good in moderation would be far better than making sugar more expensive. If anything then make fruit and vegetables cheaper.
I personally think there should be tighter regulation on "diet products" because most of them are filled with nothing but crap, and are worse for us than "normal" food. I also agree that fruit and veg should be cheaper too.