[HollowScar]

Exactly. In Ernesto's case, he had to create a revolution, to go against the government. Part of revolution is bloodshed, and he was very serious when it came to order. In Lelouch's case, Lelouch was a bit watered down, as he did not kill the Black Knights for disobeying him. Even though he could have killed Shirley, he waited, and her naive personality, and good hearted soul won him over. Unfortunately, she was sacrificed in another way. He was also planning to kill Rolo, after using him, but Rolo died as a sacrifice. He could have been much worse, had these good hearted, loyal, characters not intervened.

Regarding signing a peace treaty, the world is too naive. Peace treaties have been signed before, and have failed. If Lelouch signed a peace treaty, and moved on, he would have eventually died anyways. After his death, someone else may change the system and cause more problems. This may happen twenty years from Lelouch's death, or hundred years later. By choosing to be killed, he made it clear, that no matter how powerful a person of authority is, that person will be dealt with if he/she causes more havoc. He basically set a standard, so that the future emperors will know what happened to Lelouch vi Britannia. They will know what Zero symbolizes, and they will fear him. Just like Ernesto is a symbol, so is Zero. These symbols will keep on inspiring people, and show that it is possible to have justice.

When it comes to death, every war has its casualties. In history, if changes were to be made, there had to be bloodshed. Had Lelouch come back, and beg his father verbally to make changes, his father would have laughed it off. The price may have been tons of death, but the reward was equality, and justice for many years to come. The epilogue makes it very clear.