In note 23 to Chapter 8 of Popper's Open Society, Popper says that Russell "has shown the connection between a relativist theory of truth and the creed of fascism" (Princeton U.P., 1966). So, I haven't read the Russell, but here is a Popperian-inspired argument for this conclusion. Tarski made truth talk respectable. Truth talk within science is o.k. provided we employ Tarski's predicates (or something similar). The "truth" of the relativist is not Tarski's "truth". According to Popper at least, Tarski's truth is absolutist and correspondence (see Open Society, p. 273, note 23.). Hence, relativism's "truth" is unscientific. Fascism is unscientific insofar as it exhibits historicist tendencies--viewing history as exhibiting lawlike behavior such that if one knew the laws governing history one could predict history's culmination. Relativism's being incompatible with Tarski but compatible with fascism justifies our rejecting it.
But, many (Horwich, Field) argue that we can get by with a deflationary conception of truth in science. We just need a certain logical device to enable us to make blind ascriptions, convey our assent to a large (potentially infinite) set of sentences, and so on. So, if this is the bare minimum we need, then it looks like we cannot rule out fascism using only our theory of truth and our theory of science. But this is what we'd want. Our theory of truth may inform other areas, such as meaning, but it seems improbable that our theory of truth would rule out a political view such as fascism. Fascism stands or falls on its own. But, and here is where I'll end it, does fascism require a certain notion of truth? Can one be both a fascist and an absolutist or a realist or a correspondence theorist? I see no reason why not.
[B.T.W., most of my posts will not be political, but I've had this on my brain lately as I'm teaching the Popper to my students.]
Are you kidding? Are there any fascists that need ruling out, besides a few alienated, shaven-headed high-school dropouts in Kansas? Your logical skills, Michael, are best deployed for defeating the real scourge of freedom today: monarchists. A well-articulated theory of truth will finally displace these devils from their rule.
I don't know any fascists, but if I did then they'd need ruling out. My point, however poorly I tried to make it, is that fascism should be consistent with any theory of truth (provided the theory of truth is consistent). Maybe relativistic theories are inconsistent. But that is a problem not with fascism but with relativistic theories of truth. I guess I'll have to track down the Russell article and determine the extent of the connection between fascism and relativism. Hopefully the (alleged) connection will be something stronger that a good sociologist could find out. My money is against it, though.