That’s an incredibly dishonest put-down certain sort of people use.

For one thing, it’s not exactly easy to move to another country, not since World War I. You can’t simply pick a country and move to it - and you full well known that when you dismiss somebody with this sentence.

For another, I like my country. And I have every right to not like where it’s heading. “If you don’t like my politics, emigrate” is preposterous.