In today's World War Hulk: X-Men #3, we see the return of a character to villainy.
Read the rest for spoilers.
In the issue, Juggernaut basically decides to fully embrace his bad side in order to take down the Hulk. Since the comic in question is not New Excalibur, I do not know if this change in Juggernaut will be permanent, but it sure seemed that way, and if so, I think it would be a welcome return to villainy on the part of Juggernaut.
Don't get me wrong, I don't want Juggernaut to be a TOTAL villain, but I think he works a lot better as a pretty bad guy than as a watered-down good guy. ESPECIALLY his power levels, which have to be greatly reduced for him to be a working good guy, but are allowed to be massive when he is a bad guy.
I am mixed, on the whole, on the whole "villain becomes good" routine. I think for Emma Frost, it worked quite well. It was not like she was some major bad guy anyways.
Magneto, I prefer as a bad guy. Make him a tortured soul all you like, that's fine by me, but Magneto as a HERO just seems silly to me. This is a dude who tried to nuke the entire WORLD!!!
Deathstroke, I am torn on. Looking back, Marv Wolfman didn't even really HAVE Slade Wilson be ALL that bad, so I think some of his appearances from Identity Crisis on have been a bit much. I think Wilson works better as a mercenary - one who may be on the other side of the good guys, so he'll fight good guys, but on the whole, is not some evil bastard. But post Identity Crisis, that's basically been what Deathstroke has become, which is a bit of a disappointment for me.
The Sandman I didn't mind as a good guy, as his story seemed believable enough. I think the redemption of Sandman really began with Tom DeFalco in Marvel Two-in-One, and it worked well. It was not like there were tons of writers out there in the Spider-Man books begging for chances to have Sandman fight Spider-Man.
Kurt Busiek chose well for the villains he turned into heroes in the Thunderbolts, as Goliath, Beetle and Screaming Mimi did not exactly have the most sterling "I am clearly a super villainous person" backgrounds. I believe Gerry Conway had a great Beetle story where he made the Beetle pretty sympathetic, really. But then the Beetle killed someone outright in one of the Sinister Syndicate stories, which I thought was kinda wrong.
Goliath was always more of a mercenary than anything, so his redemption was okay.
Hmmm..."something makes me go crazy sometimes," isn't that the excuse for Magneto, Namor AND Radioactive Man? Weird.
In any event, I guess there really is no definitive answer on whether a character should become a hero or not, but I, for one, am glad that Juggernaut at least appears to be on the side of "not exactly the angles" once again.