The one show stopper for you, been mentioned already but again now for posterity:
Security. <===
Your idea is fantastic, but to implement it you need some way to securely identify unique humans, a nontrivial problem.
Until we have this down, we will be wasting our time.
That is of course an interesting problem to solve. It would require keeping a national database with biometric data (actually the EU kind of has one - most of the passports nowadays are biometric). Of course, hackers could pose a problem, but with sufficiently strong encryption and a transparent mechanism open for public auditing, I think it should be ok. Just think the bitcoin system, which is relatively immune to tampering attempts because of its open source structure.
Yes, encryption and open system could help, but I don't see the solution. Until there is a secure implementation, there isn't one yet
This is indeed related to the bitcoin system. However, Proof-of-work, or one CPU one income, works because you can prove you did some hashing. However proving you are a human I have a feeling will be a trickier one and will wind up as a game of whack-a-mole as Gavin would say.
The idea of a "national database" would of course have to be replaced by something public like a block chain data structure so to avoid regulatory capture phenomenon and the blatant security hole of letting some folks change the database at will. I have no idea how an "OP_ADD_HUMAN" transaction would be verified. It might need to wait for some kind of universally trusted AI to come along and welcome us all to the human polity
IMHO other economic arguments for or against are rendered moot if there is no secure implementation with which to implement the system.