The Penguin is arguably a 'professional' - he may consider himself an aristocrat of sorts, but at the end of the day, all he really wants is a chunk of the pie and a steady cash flow. Harley also seems like this kind of crook, when she's being a crook - during her solo book, when she had her own team of henchmen, she seemed to focus largely on simple (if ambitious) 'rob from the rich people' sort of schemes. She'll happily go ALONG with other sorts of schemes, if she's teaming up with someone or hooked up with her Mistah J, but she's largely got fairly simple needs. Also, Killer Croc has always struck me as a fairly blue-collar kinda guy. Still, though, when most of your villains live in an asylum, it's unavoidable that a lot of 'em are going to be maniacs.