Tether is how you short bitcoin -- it's hard to move USD out of exchanges, people are worried about a bitcoin (or "all cryptocurrencies") drop, so they move into tether hoping to buy back in after bitcoin goes down without having to do the expensive/difficult bitcoin-usd move.

This assumes that the price of bitcoin will go down but the rest of the system (exchanges, tether, mining, etc.) will stay intact.

As long as people want to short bitcoin there will be lots of demand for tether at a little over a dollar that the tether company will be happy to supply. These people will balance out anyone who wants out of tether in the short term, and it's impossible to lever your "tether goes down" position.

In the future, when people decide to turn around and sell in bulk for a little under a dollar, tether might not be able to make good, particularly if they were holding their balances in bitcoin instead of USD like they claim.

Bitcoin shorters might be willing to gamble that they can move faster than the tether market will collapse in that situation and not be the bagholder.

There's no way to short "the whole mess" aside from just not getting involved in the first place or trying to get your money out while you can.