Well, 'sin' is a subjective construct of a conscious mind, and science can view it as such (and it does, in epistemology and more commonly in the social sciences).

In any case, this is pretty much the same for the issue at hand. 'Humanity' and 'life' are subjective constructs. Some societies view life as beginning after a child reaches puberty.

Therefore, each individual can subjectively define what is life, and what lives are permissible to be killed. Hell, even 'killing' is subjective. There are Guinean tribes that don't consider and individual dead until several days after being medically defined as dead.

But while every individual can take his own interpretation, when humans come into a collective, a natural occurrence is that a common set of rules are imposed on the collective. Hence, the willingness/unwillingness to kill animals etc. etc.

cheers