Who gets to decide which forums are proper and which aren't? Should we ban flag burning, but allow Koran and Bible burning? Those are "acting" too. Surely burning a bible is more offensive than burning a flag? What about cross burning?
You're arguing a literalist argument for the sake of argument, outside the context of the intent of my statement, and/or the law.
It appears you are more concerned with your individual right to scratch your ass in public than appropriate public decorum. A proper forum would be a setting where an individual/group of individuals can voice their grievances to the appropriate officials in a reasonable manner. Burning the symbol of this Nation is NOT voicing a grievance in a reasonble manner.
I do not advocate the desecration of anything solely for the sake of sensationalism/getting some attention.
I agree that a sidewalk is not a proper forum for flag burning, mainly due to the fire code. It should be restricted to private property. Of course if I had my way, there wouldn't be much of any public property, and private road and sidewalk owners would decide if they want to allow protestors and flag burners, but that's a different thread.
Should peaceful-but-subversive propaganda be allowed?
Would I personally allow it? No. Is it allowed by law in this Nation? Yes.
The constitution isn't a document which lays out a list of what you may do, or a document which states that the government may do as it pleases except for X, Y, and Z. It's a document of enumerated powers, where the federal government is allowed a short list of things which it may do, and nothing more. And deciding what constitutes acceptable expression is not on that list. Granted, this principle has been increasingly ignored for 70+ years, but that's what it actually says.