I disagree. 17 years after creating an Amazon account, I've reviewed only a handful of my purchases from them (in all that time, I've posted a whopping 53, according to my profile), and I'm certainly not one of the far-too-many people who believe themselves obligated to post reviews (or answer product questions with "sorry, I don't know, I gave the XYZ to my son in another state") just because Amazon or the seller sends me email asking me to. But I do think thoughtful, detail-oriented user reviews are often more helpful than many "professional" reviews, and Amazon certainly encourages and even solicits them, and if I do bother to write one that doesn't in fact facially violate their loosey-goosey TOS, I think it should stand or that I should at least be told in something other than totally vague terms what's wrong with it...
That being said...
I have to agree that several things sound really fishy here. (And if Amazon actually "bans" people they think are shills, I'm actually glad to hear it - even if they do it unfairly from time to time - since the general impression I've gotten is that except when they're publicly exposed for it, they all but tacitly encourage it, to boost their own profits... Yes, I'm afraid I am that cynical.) ETA: Also, fwiw, "appalling" is an awfully strong word. I find it "appalling" that 50% of the US electorate voted for Donald Trump for POTUS. Amazon hiding one's reviews, on the other hand, barely registers as "annoying"...
I once had some of my reviews "hidden" by Amazon. But they were for books I had not bought on Amazon (or anywhere, thankfully, I'd borrowed them from my library) and they were anything but positive, bordering on what I suppose a hypersensitive type might've considered "personal" attacks on the authors/copyright holders, and I hadn't written all that many other reviews in general at that point. Otoh, they certainly didn't hide all my reviews, nor lock down or do anything else screwy to my account in general. I did complain, or rather asked rather pointedly for an explanation, but of course I didn't get get one (nor for matter did I actually expect to.) For a while I totally boycotted Amazon reviews, not posting any at all and myself "hiding" all of the ones Amazon had let stand. But eventually I got bored with that and started reviewing stuff again and, for whatever the reasons, the ones Amazon had hidden were unhidden at some point. (I assume, but really don't know, during some sort of later random "auditing" at which point I'd posted quite a few more reviews (varyingly positive and critical) of products I had in fact bought from, or at least on, Amazon.
If anyone is wondering, the reviews in question were slams - actually, merciless obliterations would be a better description - of a couple of the posthumous Dune-prequel so-called-literary excrescences, including comments along the lines of wondering just how desperate for money Frank Herbert's heirs must've been to have abetted the books' publication, even ignoring their participation in their authorship despite clearly not having inherited even a microscopic fraction of Frank's talent. (Although I enjoyed the Dune books, once through was enough and I wasn't what you'd call a "fan" of even Frank himself. But his books were deathless masterworks by comparison to any of the far-too numerous "prequels" that were published after his death. And since the said heir(s) had made themselves "public figures" at least as author(s) and copyright holder(s) of the books, I thought my comments weren't unfairly personal.) At some point I edited them to remove the worst of the "personal" aspects, though maybe even adding a little more content-oriented condemnation. Dunno if that was the tipping point or my having bulked up my overall review count.