Evil

[Son of Númenor]

Evil in Tolkien's world seems to me, ultimately, to be the act of setting one's self up in direct opposition to the will of the Creator - or to be knowingly subservient to one who does this. In the former category we have, as Ulmo said, Sauron and Morgoth - and, I would posit, Saruman as well. In the latter, examples that spring to mind are the Balrogs, orcs, Gríma Wormtongue, et al.

In defense of Elrond, - and, for that matter, all the Elves of the Third Age besides Legolas - it seems a truth universally acknowledged by the 'good guys' in Lord of the Rings that the Elves were 'declining' - that it was the time for Men (and, as Elrond says in the "Council", for Hobbits) to take the proverbial reigns. The Eldar, after all, had battled Sauron and Morgoth for ages, and had grown weary of fighting - and of mortal lands. What better way to pass the torch than to lend guidance and help to Men at need, (without seeking to dominate or interfere) during the battle that could prove definitive of Men's 'time' as the stewards of Middle-earth?