Ah, The cousins of the Temporarily embarrassed Billionaires/Entrepreneurs.
While, overall, Steinbeck said something different, your description of the intent is incorrect. "I guess the trouble was that we didn’t have any self-admitted proletarians. Everyone was a temporarily embarrassed capitalist." - This can only make sense when attributed to capitalists (believers in it) regardless of what systems they are currently participating in. This is a subtle description of human nature at large, which is why it's so memorable.
My interpretation is not.
> most of the so-called Communists I met
> Steinbeck positing that the reason the movement is unsuccessful as it being opposed by the temporarily embarrassed millionaires
> This can only make sense when attributed to capitalists (believers in it) regardless of what systems they are currently participating in <--- ie Communist support or however you want to constrain it
The same phrasing you repeated, reiterates my point. Good luck with whatever.