Again, no one is arguing that it isn't impossible. Like I said, in my original post, look at Dual_EC_DRBG - it was a cryptographic solution used by the NSA, that purposely had a backdoor - it was discovered by an outdoor party and now its worthless. (Look at Juniper systems (used by the USG), a very recent example of how this backdoor has failed).
I'm not a cryptographer, but lets assume a multikey solution is 100% possible.
The very notion that you can trust the government with a global key to all encryption is the crux of the issue. How do you know that Donald Trump won't wake up tomorrow and sell that key China? What do you then do if Germany then demands that key? What if Congress decides that giving Israel he private key is important to stability in the middle east? Then what do you do is some nationstate sells this key to a blackhat organization? Welp, all of Google's encryption is now worthless because this "multikey" that was supposed to be for the USG ended up in the hands of a blackhat - and now we have another Fappening 3.0 on our hands.
Great now the whole world has this "multikey" making it virtually worthless because the entire world can decrypt it. If you as an end user cannot control who can and cannot decrypt your messages, then its worthless as an encryption scheme.
Its not a technical issue, and the solution isn't limited because we aren't smart enough. The fundamental problem is that you cannot trust any third party with such a multikey.
