Good question. If we don't "love" our villains, how can we make them into real people? Fantasy writers are prone to working the good vs evil idea, with the evil being incarnated as evil wizard, evil overlord, evil dwarf, evil something-that-is-only-represented-by-a-picture-like-an-eye, etc. (There's a whole web page devoted to Fantasy/SF Turkeys to avoid.) But character motivation is as important for the villains as it is for your hero. Perhaps even more so, because the whole story arc of a hero/villain scenario is surely that until the last moment, the villain is winning. If not, the story is over. Hero 1, Villain 0. Done and dusted.
Why would someone want to rule the world? Why would someone want all the money, or all the magic, or all the girls, or all the ... whatever? If that desire is not concrete, if it's not understandable, if it's not believable - then you end up with a cardboard villain, and no real conflict in the story.
OK, so I'll use the Deaver example again. Villain is a people smuggler from China, ruthless, with a lot of contacts that he's paid for, either with money or threats. He's also very intelligent, and street-smart. He has that sixth sense about danger. He can think on his feet. He is a strong foe, almost unbeatable. He also has a history - a family of parents and brother who were killed during the Mao revolution - and a driving thirst for revenge. No one gets away with anything with this guy, no matter who they are. He will pursue those he wants to kill with everything he's got. So we have desire, motivation and intelligence. Hard to beat in a villain, really!
This is the other side of putting your most-loved characters in danger - having a villain who is not only ruthless enough to fight to the end (and hey - this is true even when you're writing a YA novel about girls competing for the same guy), but with enough layers and complexity so that the reader understands where that villain is coming from and feels, despite themselves, a little bit of pity or empathy. Now you've got a conflict that's cooking, not just for you, but also for your reader.
When is real life ever one-dimensional? When is it simple? You lie about who took the last piece of chocolate layer cake - it was you. Why do you lie? Not because you're evil (well, your kids might think so!) but because you are on a diet and feeling deprived, because you couldn't stop yourself (even though you've been preaching self-control and sharing), because you were pissed off with them not tidying their rooms like you asked, because you cooked it, and darn it, why shouldn't the last piece be yours? Lots of reasons. That's what everyone in this world is like. Mixed feelings. Mixed motivations, all at once. That's how you start to create believable characters and villains, and then you zero in on that one driving force that overrides everything else. And your story is born.