2) There is a cost associated with assigning globally-unique space no matter how you do it. This cost could be too high for some application -- RFC-1918-style space is free.
you want unique space but not pay for the administration of it. absolutely brilliant.
3) There is a concern that some recipients of this globally-unique unroutable space might use political pressure to get that space routed. This could potentially lead to an explosion of the number of routes in the global table.
look, there are two camps o v6 space is effectively infinite and the routing table can handle 500k entries easy o v6 space is kinda small (sure wish they had done variable length), and we should worry about the routing table in the first case, let them eat cake and to hell with all this yakking. in the latter case, withdraw the allocations of golden space to special services, stop allocating monsterous /48s to ethernets when we know layer-2 does not scale, stop giving /32s to anyone who asks (or whatever the fashionable prefix of the week is, i can't keep track), etc. either this thing is big enough and gonna scale, or send the turkey back to the drawing boards. but don't add already well-known disasters on top of something in which you have insufficient faith to trust to scale well. randy