the fig leak of impossibility
I don't know if I should up-vote or down-vote...
Most of what you said is reasonable... The fig leaf of impossibility however is not; and it is I suspect the reason for your current down-votes.
The the crypto boffins tell you that there is no way to build a secure crypto system that contains back doors... They do so with reason.
What you effectively doing; is wanting to go up AND down at the SAME time. It's a physical impossibility