Protectionism assumes there's such a thing as a nation state, and that introducing barriers to trade will increase the prosperity of a state. Except to the extent that a political mechanism exists by which barriers can be agreed and enforced, it has nothing specific to say about the internal politics of that state.

That's why I found the assumption bizarre. Even if there are historical reasons for assuming they come from the same place - which I think is a fair point, even if I don't agree that the reasons are all that relevant today - there's still the problem that we're really talking about a complicated collection of issues here.

Simple trade tariffs and capital extraction are only notionally connected. You can certainly have either without the other, and you can find either or both within nation states that tend towards progressive politics.

The underlying point is that thinking solely in terms of free trade vs laissez faire is a somewhat old fashioned world view when capital is bouncing around the planet at near instantaneous speeds.

"Will my CD player cost me an extra 3%?' is much less relevant to local and world politics than 'Who profits from the profit on it?'