[Mithadan]

From an old post of mine:

Tolkien's conception of Morgoth may have changed as time passed. He was originally one of a pantheon of "gods" each having their own sub-realm within the bounds of Arda (Manwe - air, Ulmo - water, etc.). These "gods" morphed into angelic Valar while retaining their pantheon-like characteristics of "elemental" power. Each had or assumed a role within the pantheon. Some of Tolkien's latest writings (the Osanwe-kenta for example) suggest that Morgoth's "role" was chaos. But rather than work cooperatively with the Valar, injecting his "wild card" into their works (the effect of chaos may have been the creation of wondrous variation in the natural world), Morgoth instead allowed his role to consume him becoming the ultimate egoist/hedonist. Instead of creating variation, he reveled in destruction and corruption. As Sharku suggests, he was not evil from the beginning but became evil through lack of restraint and utter selfishness.

Sauron suffered from similar flaws. Ironically, he is portrayed as a polar opposite of Morgoth. Sauron is portrayed as a lover of order. But in seeking to impose order in the world, he suffered from a similar lack of restraint which devolved into selfishness. Thus to impose order he uses many of the same instrumentalities employed by Morgoth to create chaos. The distinction being that Morgoth wanted destruction while Sauron wanted control. He too was not evil in the beginning but became so. As is reflected in the letter quoted by Sharku, there is no inherent evil in Middle Earth; nothing is per se irredeemable, though perhaps Morgoth and later Sauron reached a point beyond redemption.

This is from the "Inherent Evil" thread which can be found here.