In theory burning a flag is free speech and should be allowed.  The problem with burning the flag is most people are only doing it to incite violence and to try to make a certain segment of people mad.  It's no different than someone using racist language to a group of people to make them mad to incite violence. 

 

You now see burning of a flag done when members of both sides are clashing.  It provides a tense environment, puts police, people, the community in a more dangerous place.  If you can prevent these types of things from happening why wouldn't you?  If it was done during a peaceful protest that's one thing, but most people burning flags aren't doing it during those times.

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