Many people (large and small) buy tethers for all sorts of reasons.
1. Ease of moving dollars (in tether format) between exchanges
2. Safety (you'll like that one Pek!), ie if you think BTC will fall, sell BTC, buy tether until you want to re-enter BTC at a (hopefully) lower price
3. Tethers used in DeFi is a big use case as well -
https://www.hedgeweek.com/2020/05/28/285974/tether-usdt-use-spikes-growing-defi-interest
4. Merchants also buy/sell to settle business. As I said before, massive business being done in Russia, Chinese merchants selling their Chinese goods and much of it settled in tether. Also, the Chinese merchants will buy from Chinese factories, much of the trade done in tether as well. And, yes, when the Chinese are involved you can bet there's loads of monkey business involved but that's not tethers fault because if there was no tether they'd still be monkey business going on with whatever instrument is used for the transaction.
5. Random uses. Let's say we're both Americans and have a bet this Sunday for $100 on a sports team (you live in NY me in LA). I lose the bet. If we're both interested in Crypto and have accounts, why not make it instant and I send you $100 using Tether, you might prefer it that way. Of course we could also use Paypal or some other similar service so Tether is just another payment option for the market. Some will use it, others not.
As for you not buying it, that's fine, but with a $24b+ market cap, there are clearly 24billion reasons for people buying/using it.
On to Maddoff-Theranos
Yes, big time scams and certainly too good to be true with Maddoff, spitting out those 1% monthly returns like clockwork over many years. No way many of the clients didn't know because common sense says those ultra steady results are impossible. So I do agree with you that something sucessful which makes people money can blind them to the risks and/or keep them from saying anything.
Theranos not the same in my opinion because someone will crack the idea at some stage in the future (a prick of blood to determine all sorts of important health information). She just couldn't get the idea to work so lied and was then found out. I don't think she set out to scam from the beginning but ego took over when the idea didn't start to work.
But I don't agree with you that Tether is too good to be true. Yes, it's an incredible useful tool, as the ever increasing market cap and velocity of it proves, but again it's no silver bullet. The market also thinks it's a great idea as competing firms have bought out their own stable coins.
Finally, probably the smartest guys in cryto are Alemeda (rocket scientists basically), and their track record is superb. They are heavy heavy users of Tether and they have massive amounts of their own money at risk (private company). If they're using Tether, you can bet they've done some serious behind the scenes due diligence into the risks involved. So if it's good for them we can assume with pretty high odds that it's good for the general market. Here's a recent set of Tether Tweets from one of their guys -
Key point
"Having done so much of this (arbing) and worked so closely with their team (Tether team) is why we trust USDT much more than the rest of crypto twitter seems to at times"
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Big day today, the 15th.
By the close of business tether could be gone forever and that will also mean, according to many, the final end of Bitcoin...