They should already own a ton of bitcoin and someone speculated in a previous thread that their reserves are actually in bitcoin, which would make a lot of sens

They should already own a ton of bitcoin and someone speculated in a previous thread that their reserves are actually in bitcoin, which would make a lot of sense. The problem here is that every time someone redeems their tether for real dollars, Tether (the company) have to sell part of their reserves and this brings bitcoin price down, in effect dwindling their reserve pool. If there are enough bitcoin buyers or there aren't many people redeeming their tethers for dollars, they should be fine. However, if people lose faith in tether (the coin) then mass redemption will crash bitcoin prices (judging by the daily volumes of tether trading) and there won't be enough reserves to cover everyone at par with the dollar. Hence the pyramid scheme allegations. This is all assuming they don't hold $2+ bn cash in reserves.