I understand why he does it, I have gone through all the dialogue with him. It is not ok to sacrifice peoples lives and freedom for a future population without their consent. On this I will never agree, also the game really does emphasise the slavery. "A vast army of slaves". I would never support a faction that enslaved people. Their ecomony is based on slavery isn't it? That's the tribute they are referring too when they say a cannibal faction can have a percentage of the tribute. My personal opinion of caesar is that he is criminally insane and needs to be dealt with. Order and security east of vegas for who exactly?
I would have put the legate as first choice, but he's not in the game very much and I prefer to have a visible enemy.
You and I find it difficult to comprehend any need for Caesar because we live in a society where people do as they're told for the most part, a society where we have a system of established law and order. But according to Raul and what dialogue there is about the east, the lands were filled with bandits, raiders, and tribals who were a threat to settlements. According to J.E. Sawyer, the Legion and the people they oversee are two entirely different social casks. There's the settlements they oversee, like Goodsprings types, filled with Settlers, and then Legion soldiers would occupy and protect the people. However, at the rare occassion the Legion requests something of you, you're going to do it or you're going to die. It sounds harsh, but given the Legion effectively brought order to the east, one could argue doing what's asked of you by the Legion is a small price to pay.
As for ingame scenario, you have to remember, we aren't seeing the Legion as it is, we are seeing it at the frontlines. Military camps, patrols, and fortifications. The NCR is a foreign occupier as well, but the Legion is a fully hostile invader. The NCR and the Legion aren't all that dissimiliar in their aims, they both want to depose Mr. House by force and seize Vegas for their own nations. The only difference is Mr. House and NCR are more or less at an uneasy truce, the Legion has two armys to face.
Over all, my hostility to the Legion is purely because they are an active threat to Mr. House, where they to leave Vegas alone, I think the Legion is better for the East than no society.