I understand some of the context to the event. The islands had been hotly contested for centuries. The ship was outside of the exclusion zone. I understand why it could be considered somewhat of a dick move, but I don't understand people calling it a warcrime. Argentina had invaded what was largely considered British territory and were occupying it. This is the same as basically invading Britain itself, isn't it? It seems to me when you're at war, especially one you've started for no real reason other than ego, you shouldn't expect your enemy to be nice to you. The ship had shown aggressive posturing recently also. It just seems like calling this a warcrime is a stretch when the other country started and were maintainig the hostilities. I guess Britain was expected to be the more "mature" country and try to find a way to peace even though they were on the defensive? Maybe someone could put it in better context for me?
The significance of the sinking of the General Belgrano is that it was the first major loss of life in the conflict, and destroyed any prospect of a negotiated settlement. To make things more controversial, the British government made a number of false or misleading statements about the Belgrano.
International support for the Argentinian claim on the Falklands/Malvinas was widespread, particularly in South America. It was a coup of British diplomacy to gain a favourable UN resolution; the Argentinians had not been expecting opposition from the UN. However any peace settlement was likely to involve some recognition of Argentina's claim, which is probably where diplomacy over the islands had been very slowly heading over the preceding few decades.
From a British point of view, of course the Argentine military had invaded. But they had done so without anybody being killed. It wasn't yet a "shooting war" (well, it was, but only a bit). The first deaths were from attacks on the Port Stanley airfield (50+ casualties). It was the sinking of the Belgrano that was the first major loss of life.
This is significant because there was a plan for peace in progress, mediated by Peru and supported by the US. The sinking of the Belgrano effectively escalated the war and destroyed any chance of a negotiated settlement.
Linked to this are accusations that the British government didn't want a negotiated solution because of the compromises it would bring, and perhaps even to play tough for a domestic political audience.
Much of the international press saw the attack on the Belgrano as the pivotal event of the war, giving an indication of Britain's determination to avoid a political settlement, whatever the cost.
In justifying the attack, the British government was, at best, muddled, but more likely deliberately misleading. It initially claimed that the Belgrano was sailing towards the TEZ, was armed with exocet missiles, neither of which was the case. It also claimed the Belgrano was only detected 24 hours before its sinking, and the Conqueror was at risk of losing it in shallow waters, which are very questionable.
To quote Labour MP Tam Dalyell, in 1983:
the burden of proof is now on the Prime Minister to refute the charge ... that knowing the orders to the Belgrano to return to port, knowing the seriousness of intent of the withdrawal of forces by Argentina, and of their orders, knowing that there would be huge casualties among young men, without telling - let alone consulting - our American allies, without warning the Foreign Secretary ... for the sake of her own political position or reputation, let loose a slaughter, the effects of which are still reverberating around the world, to the disadvantage of our country.
Dalyell believed that British/US intelligence on Argentina was very good, penetrating both the high levels of government and their naval signals. I'm not sure this is actually true (unfortunately I don't have time to check right now) but it's not a crucial point for understanding people's perceptions. Dalyell specifically accuses Thatcher of a war crime because
She gave the orders ... in the knowledge that the Belgrano and her escorts were at that time no conceivable threat to the task force and in the knowledge that Galtieri had ordered the withdrawal of the army from the Falklands-Malvinas[.]
(From Thatcher's Torpedo by Tam Dalyell.)