The Falklands were N-E-V-E-R part of Argentina. The entire dispute was between Spain and Britain, not Argentina and Britain.
The second point is that the islands (unlike some coral reefs in the South China Sea) are inhabited and have been inhabited for more almost 200 years. The locals want to be part of Britain, not Argentina.
On what basis does Argentina think the Falklands are theirs? They never have been before and the people don't want them. So what is the basis of their claim? "Cuz we want them?"
The inhabitants of the islands have spoken: they are British and want to remain British.