Interesting article and timely since the 40 year anniversary is coming up.
Now on the subject, I don't think anyone ever seriously argued this was a war crime. UK and Argentina were in a state of war, even if undeclared, and the "General Belgrano" was a legitimate military target.
The controversy was more whether the decision to sink it was politically motivated rather than strictly military.
If you look at the Rules of Engagement the UK had set, there was:
1) a 200 mile zone around the islands where enemy ships could be sunk on sight; and
2) outside the 200 mile limit, enemy ships could be sunk if they posed a threat to UK forces.
Now the sinking did not fall into any of those categories:
1) the "General Belgrano" was outside the 200 mile limit;
2) at the time of the attack, the ship was steaming on a westerly course away from the zone and the RN Task Forces; and
3) a 40+ year old WW2 era light cruiser was not a viable or imminent threat. Even if the ship was heading for the RN TFs, it would have been sunk by air/sea forces before it ever got within 6" gun range.
If the Royal Navy was worried that the ship could be a potential threat, it could have sent word that the ship would be engaged if it did not move away in the next 12-24 hours. As you noted, the RN could also have sunk the carrier "Veinticinco de Mayo" but decided against it even though it was more of a potential threat.
What was suspected at the time was that the order to sink the "General Belgrano" was politically motivated. PM Thatcher wanted to show that the UK was not a shadow of its former self, but was still a relevant power on the world stage. Sinking the "General Belgrano" was a messsage sent to the USA, Russia and China that the Royal Navy was still a power to be reckoned with.
p.s. - amazing how quickly time flies, I remember following the war in real time way back in 1982. Prince Andrew was a hero back then...
