IF someone could be studied in order to prevent that sort of behaviour from happening I would wholeheartedly agree. That not being the case I am all for exterminating them.
I was taking Psych as my major before I decided I did not want to complete college and they cannot in any way--((they being criminal psychologists))-- link most murderous behaviour to certain life patterns. One man may have the shittiest childhood and be beaten by both parents and treated like crap in school and still end up a very useful member of society. Another man may have had the entire world handed to them on a platter and end up being a complete psychopathic murderer. Passion crimes make sense. But cold blooded random murder does not nor will it ever make any sense.
We have been studying Manson for decades and still have no clue why he did what he did.

BUT if that were to change and we could in fact learn something I would be all for it. Learn what you may and THAN kill them.