What is purity? It sounds to me like the extreme of separation: when you call yourself purely this or that, you automatically create a boundary that divides you and all you are not. Can you be that sure about anything? I mean, I know I am a decent guy, but when forced to defend my family, will I kill or not? I for one am not certain, so I can't be a pure pacifist.
Over the ages, the concept of purity has caused bloody wars to be fought, but in these conflicts there always were individuals from both sides that fought not the war but the concept of it, coming together to form new bonds. As a result, we can probably say that none of us are pure this or that, even though we are all human and alive.