I'm not sure evil is a good subject. The trouble is that the word has religious baggage and that could be a side-track to the debate. There should be a secular word to describe people who do horrible things.
<interjecting before David gets in> Scott Peck says evil is where the truth isn't. So how about non-truth? Oops, sorry, this is skeptics so we don't do Scott Peck here ;)
Definitions may be arbitrary, but taking a word (truth) that has a commonly used set of meanings and giving it an entirely new meaning that no one else could possible know unless you deign to explain it to them and which is of absolutely no use in any other context is just intellectual posturing.
If Beauty = truth and
Evil is the absence of truth then
Evil is the absence of beauty.
Now there's a resolution for debate.
Anything that leads us in the direction of Mrs T or Dubya Bush or Andrew Lloyd Webber is definitely not going to lead us away from heated shouting (or pointless consensus) rather than good debate.
Definitions may be arbitrary, but taking a word (truth) that has a commonly used set of meanings and giving it an entirely new meaning that no one else could possible know unless you deign to explain it to them and which is of absolutely no use in any other context is just intellectual posturing.
It was a brain-storming session for a new word and a generally accepted rule for brain-storming is withholding of judgment. Therefore accusations of intellectual posturing are out of place until the analysis phase starts in my opinion :)