To build on what @Khand-e said...
There's a recognizable life cycle to all mass movements. They start with a core of intellectuals who reach out to other intellectuals. And those people reach out, and so on.
Various things, usually social upheaval, but sometimes sudden demographic changes (as in the US in the late 1960s and early 1970s) can cause these movements to become mass movements. Mass movements attract people mainly because they are trendy and fast ways to get social standing, and sometimes money and power. This process inevitably waters down the original intellectual core of the movement, and accumulates all sorts of dubious hangers-on.
Pierre Sprey is one of those hangers-on.
The original proponents of military reform in the US were upright and respectable men with at least a few good ideas. The subsequent disaster of the Vietnam War, however, was the upheaval necessary to turn the Military Reform movement into a mass movement. Soon it wasn't just fighter pilots, engineers and mathematicians (you know, people whose opinions would actually matter) coming up with bright ideas on how to improve the US military machine, there were all sorts of armchair experts and that most objectionable group, journalists.
If you know a little about aerospace engineering (and I do... know a little), and you read Pierre Sprey's work it becomes immediately obvious that the man both has no idea what he's talking about, and that he's dishonest. A good example is his monograph from the 1980s on fighter aircraft design. He completely ignores the elegant Energy Maneuverability Theory that Boyd came up with, and instead focuses on absurdly simplified metrics for fighter maneuverability like plotting wing loading against thrust to weight ratio. The entire point of Energy Maneuverability Theory is that it uses the drag polar and acceleration of an aircraft to create a continuous curve that shows all possible specific excess power conditions in the combat maneuvering envelope. By going to single-point performance criteria Sprey was going backwards, to the very sort of limited performance metrics that Boyd had made obsolete before!
He's very good at coming up with fake explanations about weapons systems that resonate with non-experts because he is himself a non-expert. In his fighter design monograph he decries the new generation of low-bypass turbofan engines then coming into service (GE F404 and P&W F100) as the playthings of "technologists." He takes particular umbrage at the use of the new mono-crystal nickel alloys used in the high pressure turbine blades themselves, on the grounds that they are expensive and difficult to produce (they are). But where he goes completely off the deep end is when he claims that the fancy alloys don't do anything, and the old engines were just as good as the new ones. Seriously, he says that, on page 151.
This is fucking contrary to thermodynamics. The entire point of the high pressure ratios and turbine inlet temperatures is that they improve the efficiency and power density of the Brayton Cycle. But Sprey thinks that Pratt and Whitney and GE threw hundreds of millions developing new engines for yucks. So what evidence does he have to support this idea?
That's where he gets dishonest. He cites, for instance, DACT exercises between F-15As and F-5Es where the F-15 had notably worse combat endurance, and that the F100 engine doesn't have dramatically better performance than the old J85 in the F-5E. Only he doesn't mention why. It turns out that the early F-15As had fidgety engines that weren't totally debugged. They would stall sometimes, wore out more quickly than anticipated, and the ignition on the afterburners wasn't very reliable. As a temporary expedient while Pratt and Whitney could work out permanent solutions, the engines were de-rated and lost about 20% of the thrust they were originally speced for, and in air combat exercises the pilots would frequently just leave the afterburners on at the lowest setting all the time to avoid the re-light problems. I stumbled upon this full explanation in a book by Mike Spick. How could Sprey have known about these anecdotes but omitted the explanation? I don't think he could have. He was clearly omitting facts to deliberately further his own (stupid) ideas.
He's a waste of space.