The question gave me a bit of a chuckle: the admiral's name wasn't Labourde (which means "blunder" or "boner" in French) but Laborde.
Anyhow, rs.29's answer contains most of the key elements. I'll add a few more:
- On the international scene, Vichy had adopted a neutral stance and didn't want to be dragged back in the war. France and Germany had signed an armistice treaty, which meant that they were officially still at war against one another, but hostilities were suspended provided both parties respected the conditions of the treaty. Sending the French fleet to rally the Allies meant violating the armistice, which in turn meant that the Germans would be perfectly justified to resume hostilities against France and impose far worse conditions than before.
- The French admiralty and sailors had spent the last two years with a mindset that they should scuttle in case their ships were seized. Indeed, in article 8 of the 1940 armistice treaty, the Germans swore they had no intention to use the French fleet, but the French admiralty never believed for a moment that the Germans would keep their word. A permanent order was issued to the entire French fleet to make preparations to scuttle at a moment's notice in case there was an attempt from the Axis to seize ships. This order was repeated at various points and never rescinded. This would explain why Admiral de Laborde didn't waste much time in giving the order to scuttle, and why the French sailors didn't waste much time in executing it either. When the Vichy government wanted to avoid causing an incident and attempted to cancel Admiral de Laborde's order, it was too late.
Finally, the justifications given by the Vichy officials themselves might be worth having a look at, although they have to be taken with a grain of salt. I translated below an excerpt of the defence Marshal Pétain gave on this topic during his trial:
To answer the question about the scuttling of the Fleet at Toulon on the 27th of November 1942, we need to go back in time. The Armistice left out Fleet largely intact, but unarmed and under guard. She remained our property. In order to prevent a violation of the Armistice, either from the Germans or the English, and to satisfy the commitement we had with the later at Cangé(*), we gave orders to prepare to scuttle on the day of the Armistice, and we never recinded these orders. The agression at Mers-el-Kébir on the 3rd of July 1940 allowed us to obtain a concession from the Axis that we constitute a "High-Sea force". Our orders to prepare to scuttle were maintained. After the Anglo-Saxons disbarquement in Africa, on the 11th of November 1942 the Germans invaded the Free Zone. My governement managed to erect around the Fleet a last defensive wall by obtaining from the German high-command that French Navy managed the defense of the camp of Toulon. Also, in the terms of the secret treaty I negociated with Mr. Winston Churchill, it was stipulated that our fleet would scuttle rather than fall in German or Italian hands. On the 27th of November, when a German tanked division entered in Toulon's camp and tryed to capture our fleet, Admiral de Laborde gave the order to scuttle, as per the permenant orders that were given, as well as the comittement we had taken with the English, as well as maritime justice. The French Fleet didn't fall into Axis' hands. Why did I not give the fleet the order to rally Africa as early as the 11th of November? That order would not have been executable for technical reasons and our fleet would have been doomed to be destroyed, so letting the fleet depart would have had the same consequences than sctulling. Besides, such an order would have meant resuming hostilities with Germany and expose a disarmed France to terrible reprisals with no benefit whatsoever for the Allied cause. Between two evils, a politician must chose the lesser. To me, the Fleet scuttling as per our comittements was less serious than sending her to her doom and allow unprecedented violence being unleashed upon France, and see the 700,000 prisonners whose liberation I managed to negociate being sent back in captivity, and a "gauleiter" replacing the French governement. Therefore, I avoided the worst while helping our common victory, preventing Germany from increasing her war potentiel by capturing our fleet. Still, I consider this unavoidable scuttling as a sacrifice and a national mourning.
(*) Pétain is referring to the fact that in 1940 the French had sworn to the British that the French fleet wouldn't fall in German's hands.