Originally Posted by
Enkidoh
Going on a tangent slightly here but the idea of snakes being 'evil' is more a Western/Judeo-Christian concept (due to a confusion of the Biblical story of the Fall of Man being caused by a snake tricking Adam and Eve into eating the Forbidden Fruit with the seperate idea of Satan as an enemy of God), as there are a number of cultures where serpents are not evil, but benevolent (Australian Aboriginal belief for example, the Rainbow Serpent is a creator deity responsible for creating the entire universe - read: the Australian landscape). Snakes being evil beings has probably come about simply due to their cold-blooded nature as reptiles and how many snakes (serpents included), are not only highly venomous but downright aggressive - it's not hard to then take that further as making them into an evil flying menance tormenting the 'just and good'.
Seiryu being based on Chinese/Japanese mythological ideas thus makes sense - dragons in many Asian cultures naturally being regarded as divine entities and Seiryu as a serpent Auspice in an Asian-counterpart culture fits the bill nicely.