Because there were 1.2 million of our armed forces who died for that flag.  It represents freedom.  The hard won freedom for you to burn the very symbol that represents that idea.  The idea of freedom.  Go ahead and burn it in front of me; I will stop you.  Many of my friends will help me, too.  Just because you can, doesn't mean you should.  Didn't your mom teach you that?  Shameful.  Just utterly shameful.  Men & women right now as you are reading this are working to ensure and insure your right to protest them in any legal reasonable way, shape or form.  Ironic, huh?  Some of them face enemies, both foreign, and yes, domestic, too.  Just so you can comment on a website.  Freely.  Without much worry about whatever it is you want to say or do.  

Your welcome.