I consider both flag burning and book burning to be idiotic, but consider it a right as a citizen to do so (provided they own the flag/book)....there is a difference between calling the pastor a misguided idiot and saying he doesn't have the right to be a misguided idiot..
If the country that flag represents is bad or if a book is very bad, I think that burning that flag or burning that book would be a valid form of protest. The opposite opinion I feel is just conventional wisdom and politically correct procedure.