I think we should allow it as a vital expression of the 1st amendment. The flag is a symbol, an emotional one for sure (as is the case with most flags) but it stands for a country that is great because of the rights that are set forth in the Constitution. The same constitution you swear to uphold in your enlistment oath (notice the absence of the flag):
I, (name), do solemly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I will obey the orders of the President of the United States and the orders of the officers appointed overme, according to regulations and the Uniform Code of Military Justice. So help me God.
Personally, I don't think there has been a valid flag burning issue in my lifetime, and I hope there never is one. While some events have been disagreeable to portions of the population, they have typically not strayed outside of the bounds of legal government. At most flying the flag upside down or burning an effigy of a political opponent would be appropriate, IMO. But, there are idiots everywhere, and once or twice a year some idiot who probably couldn't argue his or her point past a few poorly understood slogans, decides to "make a statement." Usually in order to get laid, IMO. But, the right to this form of expression stands as a symbol to the world that the day a true patriot might be willing burn a flag in protest is still a long way off. I wonder if any of our founding fathers burned an English flag back in the day.
However, since it pisses us off (myself included), we once again contemplate trashing a fundamental right of expression, something that sets America apart from so many countries in the world. All because of a few idiots who would be better off ignored.
Charon