Luthien, Huan and Sauron

[Galorme]

I do not believe Tolkien ever wrote an execution executed by the good side (I might be wrong on that).

There have been a few, Melkor's Messenger and indeed Melkor himself had their bodies destroyed by the Valar. Oh yeah and Eol the dark elf for killing his wife was executed by Turgon. Maybe you would count Barahir by Turin, but maybe not.

But i agree, to kill Sauron would have been to resort to the tactics of the enemy. There was nothing to be gained by killing Sauron as they were not in any immediate danger from him, and to kill him because he could cause evil in the future would be wrong. What if Elrond had executed Boromir because he felt he was too proud and may be tempted? Its like the Hitler question: Would a true good person kill Hitler as a small child who had at that point done nothing wrong (yet)?