[Angus]

The difference being that Thatcher sent our troops to defend an illegal invasion by the Argentinians upon BRITISH citizens. There was no deception or ambiguity about the reasons for the deployment of our troops, and in fact the Falklands War boosted her popularity to such an extent that she was re-elected in 1983 and 1987.
You have mentioned Resolution 502 but have omitted the full terms:

Resolution 502, which was in the United Kingdom's favour, gave the UK the option to invoke Article 51 of the United Nations Charter, allowing it to claim the right of self-defense. It was supported by the European Economic Community, which later imposed sanctions on Argentina and by the members of the Commonwealth

So contrary to what you imply the Conservative Government, brilliantly led by Margaret Thatcher, acted properly within UN law. It is no surprise that in 1983 her government was returned with a landslide.