Well, Do we challenge the idea that Britain has power over Falklands today because it was a colonizer? Did the Penguins ask Brits to go there?
The same about all the nations which claimed sovereignty they all were hunting for new territories, some of them still do have colonies.
Self-determination? are you serious about this? Brits saying no to Britain?
It is like asking an adopted child who does he want? a mom with whom he lived all life or real mom who he has never seen in life and who is ugly and poor?!
UN Security Council of course is a tool in hand of Britain, as UK enjoys the veto power.
And Lisbon Treaty recognition makes the subject more dodgy, as it could not be fair, as UK is a part of the EU not the Argentina and this recognition is a subject of political bargain which UK got from other 26 friends of the club to make its 'argument' stronger.