I think you're both over-looking that there are people out there who just love to cause strife and chaos and don't care about right or wrong and are incapable of having "weak moments" because they have no conscious. In actuality, yes, some evil does exist just for the sake of "evil". Ergo, it would be no negative to have a fictional character just like that.
And who says a villain we don't know much about can't be clever? Jafar from Aladdin has no specific history to speak of, but he was very clever. And I defy anyone to say that the Joker from The Dark Knight wasn't a great villain, and we don't know squate about him or his motives.
The villain I have in mind does have a motivation: to watch gleefully as the world burns because he's frikkin insane and derives a sick kind of satisfaction from it. Its not very specific, but its still there. Why wouldn't this fly with you two? Just because he doesn't have a backstory doesn't mean he can't be a 3D villain. As I said, it all depends on how well he's played out.
Drake, I don't want to be rude, but I have to be frank. The kind of thinking you presented sickens me. I know its a matter of taste, but the idea of feeling anything other than contempt for such a figure just makes my skin crawl. I will be saving my sympathies for Samwise and Frodo instead of Gollum, thank you very much.
It is not a plus if the villain thinks they're doing the right thing. They'd have to be pretty stupid to think that killing millions of innocent people, disrupting the order causing the world to fall into chaos, supporting an ideal that sacrifices those not considered "important" aside to thw wolves, trying to destroy the world, trying to take over the world, trying to force an idea of others, or whatever, and the like is the right thing. And I'd be even less inspired to feel sympathy for one who did, because at least the unsympathetic villains are fully aware of the consequences of what they're doing. They just don't care as long as they get their way.
A villain does what he/she does out of personal and selfish gain. To think that someone who destroys, conquers, lies, and steals could be a sympathetic figure is just naive.
If there is character growth and sympathy to be had, let it come from the heroes. The villain should always take second fiddle to the characters we're primarily reading about or watching, anyway.
Conclusion, I know I was pretty rough in this post, but you have to understand that in the case of the villain, talk of sympathizing with the figure who summoned up a meteor to strike and destroy the earth or back-stabbed his way to the top is just something that puts me off very quickly. Its one of those things in fiction I feel strongly about. The way I look at it, if you feel sorry for the guy whose already destroyed about a dozen planets, I just think you're more likely to be fooled by a real life trouble maker. That's why I don't let myself take a sympathetic stance on it, because how we look at fictional DOES and WILL effect how we view the world. And in real life, I can't name a single lowlife or warmonger who did any of the things they did out of a remotely understandable motivation.
But, there you have it in a nutshell: sadistic, unbalanced villains are not and should not be tragic figures. They are little people. They are not Sephiroth.