The OP on snort sounds braindead. NIST defines a backdoor to be an "undocumented way of gaining access to computer system." There is nothing undocumented about this, it's literally in the whitepaper on the official website. The whitepaper also says the offline signing keys held by Blockstream need the cooperation of the corresponding participants to decrypt. It also says the emergency keys can only be used after a relative timelock.

Liquid still requires trust in the federation and is different from Bitcoin in that way, but being conspiratorial about an openly documented thing feels like engagement farming.