I think it’s interesting to look at the patterns of historical usage mentioned in the wiki. The phrase always originates with an accusation by party A that party B calls party C useful idiots, but there’s never any evidence backing up the accusation against party B. To me it just seems like a condescending way of dismissing party C - essentially an argument meant to invalidate popular support for party B. It’s not necessarily wrong, but I think without evidence it’s essentially a tactic for party A to deal with the cognitive dissonance arising from their distaste for party B combined with party C’s support for party B.

Now I’m getting in the weeds and questioning the motivations of party A. I suspect this might make party A feel the way party C does when people call them “useful idiots”. And perhaps it demonstrates how this line of questioning is an endless rabbit hole.

> The phrase always originates with an accusation by party A that party B calls party C useful idiots, but there’s never any evidence backing up the accusation against party B.

I think the criteria "that party B calls party C" is actually pretty irrelevant to the concept's usefulness.

> essentially an argument meant to invalidate popular support for party B

In most of the cases where I'd use the term "useful idiot" the "party B" doesn't have much popular support, but is rather engaging in manipulation, disinformation, dishonest propaganda, etc. The realization isn't useful as a dismissal, but rather as a reminder that you need to confront both the idiot's sincere belief along with their ignorance of it's goals, implications, and beneficiaries.