That capitalism spreads and indoctrinates its crop of managers from the middle class (bourgeoisie) to run its businesses or own them means that these subclasses, but especially the latter, are trained and rewarded to think in strictly sociopathic ways. Businessmen are encouraged to embody their businesses, and businesses in capitalist systems have only one moral: profit, which corrupts into greed when on a chronic scale.
This kind of conditioning would profoundly transform the person adopting this thought process/attitude.
So these populations, too, would be vulnerable to fascism, because fascism is a system powered by sadism, and sociopaths would gravitate to that environment.
Capitalism trains sociopaths, and sociopaths are drawn to fascism/totalitarianism in this model. So which would be the mediating variable? I believe capitalism would, as the amount of sociopathy encouraged or required for the role of manager/owner would vary, depending on the nature of the individual business in question and/or how profit driven it is (especially if profit is pursued exclusively).
Capitalism creates devourers. Mainly male in this patriarchal hierarchy, business cultivates a particular brand of masculinity that is rather Type A driven but at the very least conforms to traditional gender stereotypes (for males, this means no showing of excessive emotion; no showing vulnerability, etc). Society will culture their young boys to fit that mold, thus ensuring the next generation of people, mostly men, trained in the thought processes of sociopathy. Society conserves sociopathy.
So, just to recap: sociopathy is a susceptibility for conversion to fascism. Adoption of capitalism as an embodiment (the owner class, petit bourgeoisie) also constitutes a vulnerability to fascism, separate and apart from sociopathy. The two found together in the same individual probably compound the effects of each to the other (sociopathy ⇋ capitalism).