The issue isn't only about what happens to the finds, it's also about what gets damaged/destroyed during course of extracting them.
A find of this nature is made much more valuable in its proper, preferably undisturbed, archaeological context. The fact that you can dig it up and polish it doesn't mean that you should.
You can pick up "antiquities" all over the place, hand axes, Egyptian statuettes, Roman coins, etc. But unless you know their provenance they are effectively worthless.
Unless you're digging into a monument that's about to be destroyed anyway (for example due to the wonders of our planning laws and the disregard they place on heritage), there's no real excuse for excavation, unless it's very controlled and everything is recorded. Even then, by nature excavation is destructive to some degree. Rather like the other thread about votive offerings, I'd much rather just see the monument left alone (although I have no problem with a spot of judicious stone re-erection).
Enough monkeys with typewriters can write Shakespeare, so enough monkeys with metal detectors will sooner or later find something shiny to dig up (erm, not sure where I'm going with this now, so I'll shut up).
:-)