The fact of the matter is that UBC's would be unenforceable without registration and the anti's know this just as well as we do. If you think for one second that the anti's wouldn't go for UBC's without registration out of some sort of all-or-nothing mentality, you're sorely mistaken. Let's be frank here, the movers and shakers within the gun control movement including Feinstein, Schumer, McCarthy, Rush, Soros, and Brady all have the ultimate goal of a complete ban on private ownership. This has been the goal all along but they know that it's too big a pill for the American people to swallow all at once.
Because of this, they choose to attempt to implement their agenda incrementally rather than in one fell swoop. By slowly whittling away, they can make their proposals seem "reasonable" while telling you that they're only after those evil machine guns/saturday night specials/assault weapons/gun shows/etc. The anti's would gladly take UBC's without registration because they'll simply wait until UBC's don't work (they won't) and then push for registration so that the UBC's which "are supported by a majority of gun owners" will be enforceable. They'll further demonize the NRA and the "Gun Lobby" for not allowing them to take UBC's far enough. UBC's without registration today makes full-on registration seem all the more "reasonable" tomorrow.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar