The other side of this is that opponents always try to create negative associations for whatever they oppose.

So then someone whose politics favors authoritarianism and centralization will propose some federal power grab, opponents will make arguments favoring local control and the authoritarians will try to tar them with slavery and Jim Crow even if the subject is unrelated, e.g. whether the FDA should be overruling the states on whether or not to ban a thing in their state.

It's essentially an attempt to prevent anyone from taking the neutral position by making an accusation of guilt by association. Nazis are bad, Nazis built roads, therefore roads are bad.