Extract from “Treasures of The World The French Kings”, Written by Frederic V. Grunfeld. Select Books, A Division of Time-Life Books, B.V. Amsterdam. Great Britain: 1983.

Amazon eBay: Robespierre himself, in arguing for the death penalty, accepted that under different circumstances (an established republican order not under foreign invasion) he would not have wished it for Louis XVI. But in the current circumstances, the ex-king would serve as a focal point for the counter-revolution and thus needed to die. The death penalty became a litmus test to distinguish the radical left in the convention (the Montagne) from the moderates (Girondins) who had been the radical left of the previous legislature (under the monarchy). The external circumstances that radicalized the debate was the war, which was already going badly, and growing civil unrest within France. I don't think the self-interest or fear-based explanation of the death penalty makes much sense. If you're worried about what would happen to you under a restoration of the monarchy, you certainly don't make yourself into a regicide. The death penalty was a way to cross the bridges and burn them, and dare others to follow you: those who were too afraid to cross could be branded as unworthy of the circumstances. The death penalty, as Talleyrand famously said, was worse than a crime, it was a mistake. Talleyrand's very deep remark moves the focus away from the moral considerations, and Robespierre's 1790 arguments against the death penalty convince me far more than his 1792 arguments for Louis's death. The king's execution was indeed a very bad idea, from the point of view of Robespierre and his fellow Montagnards, and for all of France, because it opened a cycle of political violence that ended only with Robespierre's own execution. The death penalty simply became a tool of government and a way to resolve political differences. Naturally, this made it difficult for the convention to function as a normal legislature. If anything, it is rather miraculous that the convention was ever able to establish a parliamentary democracy, however dysfunctional (the Directoire period, from 1795 to 1799, with four coups in four years, the last one resulting in a military dictatorship). It was inevitable once a trial of the king was decided upon that he would have been found guilty, whether the charges were justified or not (and I am actually sympathetic to some of Francois' arguments from the legal perspective of late in 1792). I cannot think of any revolutionary regime or post coup government which has acquitted the leaders of the previous administration when they have been put on trial. There conviction was certain from the moment of their deposition. Furthermore, the death penalty was likewise an inevitability; who could have doubted that the alternatives - imprisonment or expulsion from the country - would have merely given a potent figurehead to the counter-revolutionaries? Political trials of this nature are always judicial murders, however they are dressed up. The acts of many of those who demanded and led the reforms of the period from August 1789 - the abolition of the constitutional monarchy would, if the monarchy had been restored to its pre 1789 state, been construed as treasonable in some fashion. What is probable, however, is that these men would not for the most part have been punished with the same penalty they inflcited upon the king. The great crimes of the revolution, and which fatally undermine anything positive that can be claimed for it, were the judicial murders of the Queen, her family (the Dauphin was as good as murdered and the princesse de Lamballe slaughtered brutally), and the tens of thousands of innocents who perished in the Terror. This was led by the very same people who had been the advocates of constitutional reform and shows their true character; they were men totally corrupted whose claims to being acting for the benefit of the country provced to be a disgraceful charade. The fact that many of them perished themselves by the very instrument of death they had established in the heart of the capital was natural justice. Unfortunately, in those days death was a routine method of punishment (in fact, the guillotine represented considerable progress, both in making everyone equal under the law, and in making the punishment a swift and painless one). The monarchy had given too many examples of how to deal with dissent. The French monarchy was no different to any other state in how it dealt with crime. The last time women were publicly burned at the stake in England, for the crime of forgery, was in the 1790s. Republics were no less inclined to exact terrible punishments than monarchies.