> I don't see anything at all that contradicts the idea of the Shire as an idyllic anarchic/collectivist society.The Shire is both an "anarchic" society (what government exists is extremely weak and has little impact) and a class society with a definite social hierarchy, which does play a strong role in organizing people's lives. The social hierarchy is not a government, but that doesn't mean it's weak and that people just do whatever they feel like without regard to it.
> resources are plentiful and everybody is afforded a lot of leisure
It's not at all clear that this is true of the Shire. Wealthy bachelors like Bilbo and Frodo, or heirs of wealthy families like Merry and Pippin, seem to have a lot of leisure, yes, but what about Sam? He clearly has plenty of work to do, as did his father before him. So do the other hobbits of their own class that they interact with. The hobbits that gather at the Green Dragon of an evening do so after a day's work; they don't idle there all day.
> This is the last holdout in a world being corrupted by lust for power and greed
While "corrupted by lust for power and greed" is certainly true of Saruman and the ruffians he gets to infiltrate the Shire, it's not at all clear that it's true of, say, Gondor. Even Denethor in Gondor, while he comes to a bad end, does not do so out of "lust for power and greed". He does so out of his despair, based on what Sauron shows him through the palantir, that he is doomed to fail in his life's task of preserving Gondor. But Gondor as a whole does not despair, nor does it go to the other extreme and use the Ring against Sauron--which, as Tolkien himself pointed out (and had several characters point out in the course of the story), is what would have happened if "lust for power and greed" had been the primary motivator.