TLDR for you friend:
$UST is not really a stablecoin, algostables are a meme. They are actually $1 debt tokens issued by the Terra network.
$LUNA went to zero for 2 main reasons:
- Death spiral bug ($LUNA mint to almost 10000x the old supply should not have been possible)
- 11B of excess $UST still exists, so can’t burn $LUNA to fix problem 1.
Therefore, because $UST is debt and there is an 11B excess of it preventing it pegging back to $1, this is similar to a company experiencing bankruptcy and failing to pay its debts (= defending the peg). The solution is buying back the debt at pennies on the dollar and burning it. That eventually brings UST back to peg and allows organic $LUNA burn to begin again for minting $UST (only after stability is regained).