Argentina have no legal rights over the Falklands where as Britain have owned it before Argentina was an official country. To add to this is the very simple fact that the people on the falkland islands want to be rule by the british.
Falklands are way better off under British control, because the British are less likely to abuse the rights of the citizens in the area, than the Argentinians.
The Brits beat the Argentinas off the islands, and the people living on it are British citizens. That makes it British enough for me.