While I have exactly zero respect for anybody with a political philosophy so sophomoric that it can be summed up with such a disrespectful, reprehensible act as burning their national flag (or that of another nation, for that matter) the right for them to do so is sacred and must be protected at all costs.
Here in the US the First Amendment cuts both ways. Just because I don't agree with how somebody chooses to exercise that right, it doesn't give me just cause to impose my own set of values on them.