Among the "useful idiots" there were an awful lot of very clever people (EP Thompson, Eric Hobsbawm et al spring to mind) who were fooled by Stalin at least for a time. And some stayed with the CPGB after Kruschev's denunciation of the old regime ... because they wrongly believed that they could change it from within and create a shiny, new improved revolution in already-industrialized countries that better fitted the Marx-Engels template than poor old Russia. When you've held a dream then disillusion is hard to accept and you might perform all kinds of moral gymnastics to continue believing. (Just look at how many bizarre justifications are trotted out by the religious when a natural disaster calls their faith into question.) Can we really say that, just because some people (like MacColl) were a bit better informed than most, they were therefore complicit in the worst atrocities? Or were they just hanging on for old times' sake and fear of the alternative?