It's useful to distinguish big-A and small-A agile. Big-A Agile is a management buzzword, something you can become certified in and certainly a scam. Small-a agile is a number of mostly common sense principles on how to approach process. It is emphatically not the process itself. While it cannot be meaningfully certified, it can be taught and learned. Someone else linked to the agile manifesto. I'm just gonna go out…
Furthermore, I think it's best to consider Agile in its proper historical perspective. When it first emerged, its principles -- as you've enumerated from the manifesto -- were uncommon enough to be novel and insightful. In this context, the Agile philosophy was a legitimate reaction to the problems of its day. Whether or not it's been an effective remedy to those problems is a matter of hotly contested argument. But one is, perhaps, inclined to be more charitable to Agile when fixing it into historical place.
In principle, I don't think it's fair to call Agile -- the core, original theory -- a "sham." Rather, the "sham" is all the rigidity, trappings, and liturgy that have grown up around Agile since it reached its saturation point. At some point, Agile started to ossify into a shadow-image of everything it was intended to fix. But I think that failing reflects the nature of its practitioners more than it does the core philosophy.