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.
I don't consider USDT a scam coin. It's a coin that is pegged to USD in a way that company behind it (Tether) should have USD and other assets in their balance. There are rumors that their asset balance is not equal to minted USDT tokens. They had audits but it didn't stop the rumors.