It has occurred to me that anyone working of a biological weapons program is either a dangerous ideologue or someone very close to psychopathic/sociopathic, so for such people to contemplate killing millions is easy. The step to doing it is not much harder.
It was seemingly easy for the generals to contemplate wiping out Hiroshima and Nagasaki, or Dresden, or for Madeline Albright to trivialize the deaths of perhaps a half-million due to sanctions on Iraq.
The low-ball estimate is 1% or folks are true psychopaths. This is based on an arbitrary cut-off. Seven billion people, 1% psychopathic = ?