I think there's a larger emotional attachment for some, especially those that served in the military and had friends die just to get that flag up the next hill, or to fly over the next objective. In this military case I suspect it's much more than a piece of cloth, it's their memories of those brothers in arms or even the greatest time in their lives.

In Nationalistic countries like WW2 Japan, Germany, modern America, a person's whole identity is contained in that flag. While the Rebel flag is traditionally the sign of rednecks for many or the love of a regional area one grew up in, it's the representation of oppression, racism, and losers from a very short span of time in American history. That last part might trigger some more than the oppression and racism parts as that's their identity one's talking about.

Even as a Canadian I'm saddened to see our flag fly with US political party flags as a protest and how it now represents a very vocal fringe segment of our society when previously we weren't as "Patriotic" with our flag waving outside of Canada Day or sporting events. This previously reserved aspect was yet another thing that was a difference to our southern cousins. It's been hijacked when it didn't have that connection previously.

This can also be equated in some ways like someone's childhood blankey being jumped on and burnt could cause some great grief due to memories of their mother or grandmother that made it. Humans have a great ability to package and attach meaning to things no matter the extreme.

Then one is up against feelings, not logic of right or wrong. Punching someone then becomes a larger possibility as it's emotionally not connected to the logical side of us.

Feelings are a hell of a thing and those burning or waving flags know this and this is why it can get the attention they want.