I think their right to talk about sovereignty was removed around about the time they INVADED the islands against the express wishes of the inhabitants! A lot of people argue that the Falklands War was a throwback to British Imperial power and a bad one at that.
I, however, see that war as a war based on protecting the isolated inhabitants of some defenseless islands against the aggression of a larger, and at the time undemocratic, neighbour who was using the war to distract it's own oppressed population from financial worries and a nasty "dirty war". Hmm... who was right. We were! The Argentinians obviously haven't learnt the lessons of that conflict.
Until the population of the Falkland Islands call for union with Argentina it is our duty to defend them against the expansionist ambitions of any other neighbour.