I've never understood this. I really like his gun, but if I want it the normal way, you got to wait several dozen hours (at least) to get the quest in New Vegas. But you kill him then and there, you get Strip infamy.
If you killed him after you recruited him while he was on stage, I might understand that. But he's just a random drifter on the road to Boulder City when you first encounter him. It'd be like killing Jerry (the Great Khans poet guy) giving you Followers Infamy before you even decided to tell him to join.