OK-
But marching generally only involves walking on a street - simple movement of one's own body, and ballet also only involves (more complex and certainly more beautiful) movements of one's own body, these are both fundamentally different than taking an object that is not a part of one's own body and changing it's composition.
They are both activities, certainly, but one involves acting upon an object, while the other is mere manipulation of one's own extremities.
Raising one's own finger or opening one's own mouth is different than intentionally destroying an external physical object.
I can see this difference as being the demarcation separating one act as protected expression and the other as a prosecutable activity.
What would you call the prosecutable activity? I'm not being snide, I have been over the stuff in my own head. There doesn't seem to be a conclusion to it...or I'm not smart enough to figure it out on my own.
(Not that it should be prosecutable, just stating the differenec in quality in one act vs. the other...)