Mere human tendency?

Many of us have heard of "The Rime of Ancient Mariner" by S.T.Coleridge.
Anyways one question that arises is,why did the sailor kill the albatross?
The answer which I was given-mere human tendency.The reason for killing the albatross was mere human tendency.He killed just 'coz at the moment he felt like killing or something similar to that.So,is killing a mere human tendency?A trait we 've inherited from our ancestors for whom huntlng was a source of livelihood.So,do we everytime have a reason,a reason sufficient enough to kill?

I remember an old story in my hindi book.It was called "Apna Apna Swabhav" or ''one's own nature''. Well,in that there was a saint who was bathing in river and a scorpion was floating away or drowning away.Now the saint took him in hand and started crossing the river.Now the moment the saint picked it up,the scorpion bit him.He dropped him and again held out his hand trying to save him.Again the scorpion bit him.And again the saint helped it.Thus it was after 4 stings that somehow they reached the bank and an observer asked him, "Why did u save the scorpion even though it continuously striked u?" To this the saint replied,"Apna Apna Swabhav" or 'coz its our own nature."The scorpion's nature was to bite and a human's nature is to save.So we both went by our own nature."

Both the stories contrasted each other and somehow being taught both I was confused as to what was or what should be human nature.

Today a cockroach peeped through the hole in bathroom and for a moment i hesitated on whether I should flush water & kill it.
But,just after a moment's hesitation I flushed water killing it and I wondered afterwards-why did i kill?
An ant's passing in our way.Take it in hand and crush it.Again why?Just like dat.But then we aren't killers(I don't think I am!).I took a stray pup as pet.I feed the birds in the morning .So then what exactly is human tendency?May be its both.Just like in Michaelangelo's carving in Sistine Chapel where the same kid who was sculpted for baby Jesus sat down while the artist carved Judas out of him.We 've both in us-the same human kills and the same human saves.

Well, mere human tendency!!!!!!!!!