Price manipulation of bitcoin is, I think, as possible as it's been done to gold and silver. That's what I don't like about Big Finance getting its hands on crypto.
Though the ETF news is initally pushing BTC higher, sending it about 30% higher since the news broke.
Yes, Tether is not a free market crypto. It's controlled by Tether Limited Inc and if that company goes belly up for any reason, or is discovered to not have backing for the coins it's issued or otherwise found untrustworthy, Tether goes to zero. Since it's not free makret, Tether can freeze wallets at its discretion and I read has done so. Though the reason is alleged ties to child trafficking. If so, then in this case it's freezing wallets for a good cause.