can i ask why burning thr flag is so bad anyway?

in britain it's actually illegal to go around breaking or altering stuff with the queens face on, like money, stamps etc. (are those souvenior things that press the coin into an oval with a stmp on it legal?) but that has to do withe the fact that they are also legal tender. yes even stamps.

is it really such a big deal? to deface a coin? to burn a flag? what's despicable about it?