Pearl? Seriously. Even if that would be a joke… "He ruined my life". That's a pretty strong sentence. If the guy searches through all passing ships for the SHs, I don't see him being your run-of-the-mill cannon-fodder character. Someone who gets his ass kicked on the run by the SHs hardly had his life ruined by them. Most of the former villains just got put into their places and carried on with their lives after that. If the guy had his life ruined, it has to be something bigger. Hence Arlong. He had his up-and-coming empire totally wrecked by the SHs and ended up with pretty much nothing left.
@Gorlom:
You seem to completly ignore Morgan, Buggy, Kuro, Foxy and possibly some more I'v forgotten.
Oh ye, Morgan too… Well, he does actually have a shot in my book. After all, he too lost quite a lot. And because we don't know what happened to the man after his boat-journey. If it does turn out to be an upgraded version of him, then we can therefore suppose that even Caroue (however the duck's name was spelled) can become strong enough to fight off Lucchi during an arc or two. I mean come on. Looking back at Morgan now, he'd best serve as a guy who'd just be one among the many flunkies that Chopper punches his way through at some point. >.<
The other three would join my list of "not enough reason", what with the same story as Krieg's. I don't see Kuro showing up here out of the East Blue (see what I did there?! xo), although he did get quite a bad deal what with several years of planning having been totally messed up. But he was last seen back with his crew, so I'd rule him out. Buggy is doing fine as it is without any unnecessary mystery-masks. Same applies for Foxy.
@Gorlom:
Didn't Wanze get his crappy looks back when Sanji kicked him through the door?
Yeah, I kinda recalled that… But... Well, it was just for the sake of personal snickers. And as impossible as it was from the beginning, it seemed like a viable candidate. He's with the democrats. :X