Because I feel having to sacrifice a creature is cost enough.
And it is, as I see it, as evil as the next mythological being. Not so much as being truly evil, unless you choose to be influenced by other contemporary works.
It is a snake. All snake-like Mythological creatures are considered evil by most folklore, legends, myths and tales. Look at Greek Lernaean Hydra or Typhon, Norse Jörmungandr or the Biblic Leviathan. There are countless examples of these in every kind of culture and you won't actually find any of these being considered non-evil (even Orochi). Also, most of them have strong connections with poison. Becuase of that, I suggest it should be better as an 
/ 
card.
Actually, not all snake mythology views them as evil.
for instance Quetzalcoatal, a winged feathered serpent, which was a generally benevolent diety in Aztech culture. Serpents are often seen as symbols of fertility and rebirth as well
http://en.wikipedia.org/wiki/Serpent_(symbolism)...
But you are right Arathanasios, there are certainly just as many myths which depict serpents as symbols of evil. And this creature I think fits that category pretty well.
Since the card is using the sacrifice mechanic in an "appease me or I will kill you" manner, I would say there is definitely a strong
or
connection here.
If, on the other hand, it simply attacked random other targets if not fed, you could argue that is simply very hungry and not necessarily evil.
