I think we are all capable of a wide variety of behavior and very, very few people are the type that will never kill anyone.  Fortunately most of us are not put in a situation where we feel we must kill.

Is anyone familiar with the old Mulligan experiements?  Where they had the phony lab set up and an actor was supposidly being shocked after answering a series of questions?  Except for a very few cases the experiment kept going until it appeared that the subject was either dead or unconcious due to the shocks.  Nice, normal people were pulled off the streets for this.  They did the same experiment and just used college women and puppies were supposidly being shocked.  Same results.