Caesar himself tells us that Lanius cares NOT for the Legion. He kills his own men, not out of tradition/motivation, he kills them simply because he *enjoys* killing..
Another twist..
Wikia entry: "When spoken to, Lanius reveals himself to be more honorable man then people claim he is, and care more for his soldiers than Caesar lets on. He states that treachery should not be relied on as a tactic, and hopes that the Omertas died after their plan to hold a coup on New Vegas Strip failed and they were discovered, as their aid in the Second Battle would have sullied the Legion. He also dislikes the amount of Legion men that Caesar sacrificed in his attempts to take the Dam, and that he would neither continue the attack on the Dam, nor lead the Legion east if it would only mean death to his army."
I'd suggest speaking to ALL characters and extract as much info as possible for arguments.