What is the reason they said USDT is a scam coin ? As long we can buy the USDT with our fiat money and sell it back, it is not a scam.
Now that many defi projects have been created in cryptocurrency, stable coin like USDT will be required to be used in their platform.
The reason is their transparency on their promise of holding the worth equivalent as collateral whenever they mint new coins and that got them into trouble and if any authority finds out they are manipulating the market by adding new coins without any collateral then the entire market collapses. So you need to be careful as we have seen many fall apart in this market.