They Always Call Them Crime Bills, but...
the crime is extorting a fee from law-abiding citizens for the simple enjoyment of a constitutionally guaranteed right. It certainly won't stop any street crimes. But it will make the purchase of a gun more expensive, thus raising the barrier to ownership just a little higher. Which is undoubtedly the real goal.
Such an act could not really be enforced retroactively, unless people volunteered to register the guns they already have. Criminals in illegal possession of guns cannot even be compelled to comply with a registration program (USSC, Haynes vs. US, 1968) because it would involve self-incrimination, so maybe that would also provide an affirmative defense to anyone who simply refuses to register their existing collections. Hopefully the mere proposal will cause such an uproar that Rahm will shelve it.
There is ample historical basis to fear, and thus resist, gun registration programs. Think Great Britain and Australia, and to a lesser degree Canada. Registration seems to inevitably lead to confiscation. Though, Hitler, Mao, and Stalin took it to a whole new level against a newly disarmed populace.
"To my mind it is wholly irresponsible to go into the world incapable of preventing violence, injury, crime, and death. How feeble is the mindset to accept defenselessness... How pathetic." - - Ted Nugent
"Cogito, Ergo Armitum Sum" - (I Think, Therefore I Am Armed)- - anon.