Parabellum.
if you believe that a British PM would order an RN SSN to sink an Argentine civilian ship approaching the FI, outside a period of war, then you really need to check whether you're putting sugar on your cornflakes, and not crack cocaine.
my own view is that the airliner theory has the massive flaw of having to land at MPA or Stanley, both places where a landing aircraft can very quickly be surrounded by lots of men armed with belt-fed weapons. however a civilian rustbucket that lands a group of political activists and media at a remote bay on West Falkland and sets up a 'las Malvinas camp' would not only be far less likely to be interdicted whilst getting there/setting up, but would not justify being machine-gunned into the water, and would be a major propaganda victory for CFK, and a defeat for FIG because a) it would 'show' that the FI was empty of people (something of an accepted truth in Argentina), and b) that there aren't enough civil poliemen on the islands to enforce an eviction/arrest, and that they'd have to rely of hairy squaddies - all on live TV.