I presume it has something to do with how you treat him when you first meet him. I was nice, used the speech option, and was subservient to him. I also played as a female character and used Black Widow to encourage him to help activate the gala event, during which I turned on all three hologram points and was always nice to him. When I saved him in the theater, he simply told me about his plan to rob the vault and left me alone.
I also have 100 speech but saved the game before speaking to him and ran through the various questions/answers and never had an option to save him - Perhaps due so something said to him earlier in the game?
Its all about how you interact with him during the course of Dead Money. He will be more hostile to you once you reach the theater if you treated him poorly. If you were on good terms with him, he wont even send the holograms after you when you meet him in the theater. Instead they will activate on their own and he will meet you later on friendly terms.
You DO NOT have to kill him.
I needa bit of help lads withsome rushes ya know like helixrush n tech spam, do you lot know anymore?http://img.photobucket.com/albums/v316/samuraifaith/mad.jpg