...Wha? Not really, and he's not really a villain per se, just really misguided and stubborn. He wants to keep the people safe, just like everyone else, he just has a different way of doing things that can be a bit questionable at times.
And when has he ever said he wanted to wipe out the people on the surface? He only left those people behind, reluctantly mind you, because it was essential to making sure that the Arc-Gurren could safely take-off so that at least a few people could escape Earth safely and there would be some hope for humanity rather than everyone dying. This is all really hard for him, and he's only just now starting to crack under the pressure after hiding it so well the past couple of episodes with his cool, calm demeanor.
Of course, this could all have been avoided if everyone would've stopped being so stubborn, listened to everyone's input and worked together. But that wouldn't be half as interesting, now would it?
Anyway, even if Rossiu was a villain, he'd hardly be the worst ever. He's just a guy with noble intentions that backfired, badly. He wouldn't have even turned on Simon if the citizens weren't screaming for his head on a platter. I mean, those riots were getting pretty bad. Someone could have gotten hurt or killed. Yes, it was a bastardly thing to do to sell his friend out, but his philosophy is all about the sacrifice of a few to save many. Not the best and most humane philosophy, but logically, it works out on paper. That's Rossiu's fatal flaw, but I don't hate him for it. I pity him.