I don't think that it's accurate to call tankies liberals.

A lot of this gets thought of on a left-right spectrum, but it's really more like a compass, with economics being left-right, and authoritarian/antiauthoritarian being top-bottom. Liberals in the US would be slightly left of center on the economic spectrum, but largely centrist on the authoritarianism spectrum. Tankies would be far left on the economic spectrum, but at the top of the authoritarian spectrum. Libertarians (or, what gets called libertarian now) would be at the extreme right on the economic spectrum, but at the very bottom of the authoritarianism spectrum. (The most modern libertarians are not actually anti-authoritarian, although they claim to be. E.g., many of them oppose abortion rights.)