The book is, indeed, silly (and basically incompetent), but I've never seen the point put so succinctly:

It seems to me absurd to suppose that McCumber’s book comes within cooee of excellence . He argues that the triumph of the unduly disengaged school of analytic philosophy in the USA was due to McCarthyism. It is a moot point whether analytic philosophy IS unduly disengaged (Russell, Ayer and Hart, for example, were notable as as public intellectuals and one reason that so many logical empiricists had to flee to America was because of the anti-fascist tendencies of their thought) , but whether it is or not, McCarthyism can’t be the chief explanation of its triumph in America since analytic philosophy *also* triumphed in other Anglophone countries where McCarthyism was either muted or non-existent. The book is typical of one of the two ways in which American scholars tend to go astray. Because America is such a big, powerful and important country, they find it hard to keep the rest of the world in focus. As a result they are prone to two opposing errors: seeking a global explanation for what is mainly an American phenomenon or seeking a specifically American explanation for what is a global phenomenon. McCumber gives an American explanation for the triumph of analytic philosophy which is a global or at least a pan-Anglophone phenomenon (though one should not forget the triumph of analytic philosophy in countries such as Sweden and Finland). There is the further problem that analytic philosophy had largely triumphed in America BEFORE the political advent of McCarthy whose glory days were from 1950-1954. Now you can get around this difficulty by defining McCarthyism more broadly to encompass the red-baiting anti-radical and anti-Communist hysteria (often with an anti-New Deal agenda) that began in the nineteen-thirties and found institutional expression in the House Un-American Activities Committee which began its sessions in 1938 as well as the its predecessors such as the McCormack-Dickstein Committee whose co-chair, Dickstein, turns out (hilariously) to have been in the pay of the NKVD. But in that case the theory becomes even more bizarre as the most high-profile victim of this kind of proto-McCarthyism was Bertrand Russell, one of the founding fathers of analytical philosophy, who was blocked from a job at CUNY in 1940 because of his social and sexual radicalism and his anti-religious writings, reducing him temporarily, to near destitution. So McCumber’s thesis metamorphoses into the claim that philosophers sought to avoid the fate of Bertrand Russell by philosophizing in the style pioneered by -– Bertrand Russell. Well that’s not quite right (someone might reply); the point is that the triumph of analytical philosophy is to be explained by the fact that philosophers sought to avoid the fate of Bertrand Russell a) by philosophizing in the style of Bertrand Russell whilst b) *eschewing the public role that Russell had played for so many years as an activist for left-wing causes*. But then it seems that what McCarthyism (in this extended sense) explains is not the triumph of analytic philosophy (which was well on the way by 1940 and which happened elsewhere without the aid of McCarthyism) but the relative silence of left-leaning philosophers on social issues that was characteristic of American philosophy in the forties and fifties. In other words, what McCarthyism explains is not the triumph of analytic philosophy in America but the retreat of those triumphant analytic philosophers to the ‘icy slopes of logic’ . (This is confirmed by the fact that in other countries, where McCarthyite tendencies were relatively weak, you get the triumph of analytic philosophy without the retreat to the icy slopes: Russell, Ayer and Hart were all pretty vocal on social issues in the forties, fifties and sixties.) But this is not McCumber’s thesis but Reisch’s thesis as developed in ‘How the Cold War Transformed the Philosophy of Scince’. I have reservations about Reisch’s book but at least it isn’t as obviously silly as McCumber’s.

 So it turns out that equally silly thread on Babette Babich's fantasies about the Continental traditions in philosophy produced several useful comments!