We know algorithmic stablecoins are new and risky. UST is backed by Luna, and the foundation behind Luna bought so much Bitcoin I believe they're now amongst the top 10 holders.
If UST loses its peg against the dollar and Luna isn't enough to bring it back up, the foundation will have to sell some of its BTC to keep the peg, which applies sell pressure on BTC and brings it down along with the whole crypto market.
Is this what's happening now already?
Looks like, yes. I tried to warn people but then I started to not care... Stable coins are a huge risk for the crypto space. The bigger they get, the riskier crypto becomes. TerraUSD was relatively a smaller stable coin when compared with USDT. If UST can cause that much pain, imagine what would happen if USDT was going down. I hope that day never comes but when or if it does, it will be much worse than this.