re: Why do liberals/leftists hate the flag and national anthem?

Because they are against individual liberties.

The modern day liberal is very much an Orwellian Socialist / Communist.

No gender, no religion, no flag. They encourage everyone to be different as long as being different is exactly like them.

If you disagree with them, you're a nationalist, a racist, xenophobic (which is ironic since they really hate religion, or a misogynist.

Liberalism truly is a disease.