The problem with Tether is that the exchanges themselves have huge stakes in it. If Tether were to lose its peg all of a sudden by a significant amount, the exchanges themselves would have huge holes in their balance sheets. They may refuse to allow redemption of any crypto during that period where they're trying to raise capital otherwise they themselves might go bankrupt. A liquidity crisis in Tether could cause a bank run at every exchange, which could take down the entire crypto ecosystem.