I think there's just something inherently wrong with Soc-Dem parties that makes them so vulnerable to chuddy attitudes, and it's not just them embracing capitalism.

It's the chauvinism. The reason why they became socdems to begin with was because of chauvinism, because when push came to shove they chose to side with their own bourgeoisie's wars over the international proletariat. And it is chauvinism and exceptionalism that continues to fuel social democracy. Because social democracy requires the spoils of imperial and neo-colonial plunder to sustain the privileges of a welfare state under capitalism. And because it requires you to believe in your own exceptionalism and superiority to think that social democratic reformism can succeed for you even though it has failed everywhere else. All of that naturally attracts and incubates reactionary attitudes, at first as an undercurrent and later increasingly overt as the crises of capitalism deepen.