I'm not American, but I feel like burning ANY flag is disrespectful. A flag does not represent the current government or whatever, it represents all the people who have ever lived in that country, who have built it and sometimes fought for it. For me it's just basically saying "fukk you" to every single citizen of that country, with no nuance and no understanding that in every single country there are people just like you. Yes, it's just a symbol, but to me burning a flag (ANY flag) is extremely disrespectful. I don't agree with the US or Israël for example on TONS of issues, but I'd never do that. And I'd be extremely offended if someone burned the Belgian or the Centralafrican flag.
(PS: to those who say it's freedom of speech, yes it is, and so is saying "Nigg*s stink". Freedom of speech doesn't make it "right" or "ok").