I've started reading a book on the Battle of Waterloo and it picks up with Napoleon leaving the Island of Elba. That got me wondering how Napoleon received such lenient terms to still be titled Emperor, have territory he ruled over, have such freedom of movement that he could easily escape exile, and generally be treated with such respect following his complete defeat by the Coalition Powers. Was there any thought to executing him, putting him in prison, trying him for war crimes (I realize probably novel in the 19th century), or at least some form of strict exile such as done after Waterloo? It seems his return to power following such lenient exile was foreseeable. I also vaguely had the impression (from the Master and Commander series?) that the British saw Napoleon as a terrible despot, the way that the WWII Allies might view Hitler, so was kinda surprised how easy he got off.
There were several reasons for the terms of the treaty of Fontainebleau being lenient in hindsight, and most of them have to do with Napoleon being one of the negotiating parties. The treaty was between the Allies and France - and Napoleon was France's legal sovereign, confirmed by three separate plebiscites. In 1814, Napoleon's actions as Emperor of the French were only different from those of the Allied monarchs in extent, rather than kind. There was nothing the Allies could accuse Napoleon of that he could not rightly respond to by pointing out a time they had done the same. Napoleon insisted on keeping his Imperial title, and since Elba was close to theoretically-allied Naples, was a small island that wasn't part of France, and was theoretically able to be blockaded by the Royal Navy, that was chosen.
The reason the Allies could not dictate more stringent terms was that Napoleon had not technically been defeated in 1814. Certainly he was outnumbered, fighting at the head of an exhausted nation, and on the defensive - but he had been in that position in 1800 and had led France to something close to victory. Terms that Napoleon and his marshals - who had forced him to the negotiating table in the first place - viewed as completely unacceptable would spur him back to military action, and the Allies still feared Napoleon at the head of the Grande Armée, even if it was by this point an almost-shattered force. Demanding his execution*, imprisoning him or similar measures ran the risk of uniting the Marshals, the army, and France back behind Napoleon - which might lead to Napoleon shattering the Allied armies as he had many times before. Imposing a Bourbon Restoration without a treaty with the Imperial government would only invite another revolution - especially since the French Army, war-wearied as it was, would likely prove Bonapartist rather than Royalist. Having Napoleon voluntarily abdicate was the only real way to remove him, and that meant he could influence terms. Further, Tsar Alexander of Russia, one of the leading allies, had what we might call a 'soft spot' for Napoleon - certainly he regarded the French Emperor as an enemy and a threat to peace, but he admired Napoleon for his tenacity and statesmanship.