If you're going to cherrypick a single example to rebut the existence of an overarching trend in the UK, you could at least pick a state with an income tax. Or, perhaps, not beat the dead horse at all and talk about Britain.

Washington state just decided that capital gains were not income, and imposed a 7% tax on them.

Besides, I don't see how the age demographics in Wa state would be materially different from Britain's.

If you're so fixated on Washington state, you should really learn its history. And also British history. They're very different places with very different politics.

And a 7% flat tax is a trifle.

Exactly. 20% is also very low. Maybe consider complaining when it’s 90% in the top bracket.