His numbers are generally fucked up.
His numbers on USSR deathtoll, for example, are twice that of Black Book of Communism - and those in that book were, by accounts of many people including some of the coauthors (who made an effort to distance themselves from the book due to this), overinflated anyway.
And generally the same logic would mean that liberalism is the reason for genocide of natives and Irish Famine, so overall ascribing every single fuck-up within a movement to the ideology of movement is rarely warranted.
I don't really want to get into it, as it's not N&P, but this comes with the territory when quest enters the era of ideologies and revolutions, so....