M-16 meet FN FAL or FN 49. Who will win? Of course no one should deprive the cops of their toys while they deny us ours.
Many Police Departments get used M-16s from their National Guard armories. Since they will spend most of their time riding around in the trunk of a squad car it doesn't matter that they're used.
I'd also trust a 3 round burst mode to spray and pray cops than a full auto weapon.