On April 3, Ethereum developer Ryan Berckmans tweeted that if we rely on UST pegs on a large scale, it could eventually threaten the solvency of all Ethereum DeFi. UST is an algorithmic stablecoin with a high risk of death spiral.
To avoid this death spiral, UST buys BTC at retail profits, also bridges to Ethereum via cross-chain multi-signature, and is trying to bridge liquidity with other premium stablecoins. For these reasons, Ryan believes UST is bad for Ethereum.