Looking back now, I have a hard time buying Emma Frost as one of the heroes. Reading the original Dark Phoenix saga compared to the comics today, she was evil on too many levels. It's hard to believe that such a ruthless and sadistic character would ever want to turn to the side of good after going that far. I've heard that Generation X explains her changes a bit more but
IMO one of the ways that they screwed up X-men was turning too many of their iconic baddies into good guys. I give certain characters a pass--Quicksilver, Scarlet Witch, and Rogue are all OK. I like Magneto as a grey character that can be friend or foe depending on the situation. Beyond that, Sabretooth, Juggernaut, Mystique, Emma Frost, etc. should stay villains, because the good guys need someone interesting to fight. I hope they never make the likes of Mr. Sinister into a straight good-guy.
Back to Emma--She ruthlessly executed her own people for failure...
She sent the goons after children...
She psychically tortured Storm without a second thought...
To be fair though, I still think that Jean should have stayed dead permanently after the Dark Phoenix storyline.