Don't be so sure.
What probably _would_ police these willy-nilly announcements,
however, are prefix-length filters on the various ISP routers.
And again, this could certainly lend itself to folks sic'ing their
lawyers on eacvh other in the name of anti-competitive lawsuits.
A mess ensues that I don't think any of us wishes to see happen.
Another somewhat important point is that we also need to conserve
routing entries. If you make a market for addresses without regard to
routability, you risk
creating a situation where you flood the world with /32's. No thanks.
I would think that would tend to police itself. Even now with things
as they are you're going to have serious reachability problems if you
try to announce anything smaller than a /24. And if routing tables
suddenly explode, I'd expect that threshold to quickly move in reaction.