Any backdoor fundamentally breaks the promise of any end-to-end encryption.

This isn't a problem of process like requiring warrants and just cause. Even if said process is designed to be perfect and is executed flawlessly, it is still hinged on a fundamental breakage of the security model a given chat software is built on. If a trusted government has a magic password that can read anybody's encrypted text messages, then it must be assumed more nefarious actors can figure out that password and use it themselves.

It creates a single point of failure that would compromise literally everyone.