All public key boxes are banned and Google regularly bans new ones . That endpoint contains the list of revoked keyboxes : https://android.googleapis.com/attestation/status
But you are providing an alibi for malicious users who, for example, might try to brute force logins from unidentified devices.
That would be one reason aside from the law. You are essentially positioning yourself on the same side as intruders.
You should personally immediately return any computing device where you have control, this line of reasoning is insane
You realize in Viet Nam this means getting a "friendly" visit by the MPS/BCA, and if you continue eventually getting branded as a troublemaker.
Hence my qualifier. I'm not trying to incite anyone into personal danger.