Because they can tell the difference between two very different things?

I don't know how assholes work where you live, but in the US some varieties of asshole would burn a US flag* if they wanted to pick a fight with people who have a reputation for giving a shit about symbols that "need to be respected."

Of course the proscribed way to dispose of a damaged or worn US flag is to burn it, but only weirdly precocious children would argue that this is relevant.

"Sit down, Billie**. That's not what we're talking about."

The kid it technically correct (but not really even that) and is also missing the much lager point. The larger point is that the act is a 'FUCK YOU,' coupled with 'what ya gonna do about it?'

*This isn't a great analogy aside from 1) destruction by fire and 2) the act of destruction being intended as a direct provocation.

**Also, Billie will grow up to become an energy vampire.