The trouble with economics is that if you get the incentives slightly wrong, people will relentlessly exploit the difference. So when I ask "but this, but that," I’m asking "have you thought of this exploit or that exploit?" Because unfortunately you can’t just ignore that they exist. Each of them needs a concrete answer, or the system will reward those who exploit it. (You can argue that’s true for the current system too, but at least it’s hard to exploit. The loopholes I listed above are all straightforward.)