A backdoor in the technical sense (which is the real topic of this whole conversation) is one that bypasses the known way of entry. For an "End to end encrypted" communication channel, a backdoor allows someone to view the communication without being on either of the "ends".
The problem is not whether the backdoor was legally mandated or not, and whether legal authorities are misusing them or not, the problem is that it exists. And the existence by itself is enough to let someone ignore any legal mandates and view the comms.
The problem is not whether the backdoor was legally mandated or not, and whether legal authorities are misusing them or not, the problem is that it exists. And the existence by itself is enough to let someone ignore any legal mandates and view the comms.