Well, if it happens like in Frozen with Hans, then nope.

Depends on how it's done. Like how Emma Swan turned evil.

Honestly I'm such a sucker for villains I'll take almost anything. xP

It really depends.

Depends really.

Only if it's done well

Yessss I consciously seek out stories like this. Pretty much a blatant villain-sympathiser xD

^ Same actually, I think it makes for a great story.

^ Well, not always. I know one example where it was an improvement but was still bad. Dark Bloom on Winx Club.

She didn't turn bad on her own accord though, so I personally do t count that. Plus it was temporary.

Not usually, but occasionally I like when they 'temporarily' turn evil. Like Void!Stiles, Demon!Dean, Ripper!Stefan, The Winter Soldier, etc.. It's awesome to see an actor/actress that's usually playing a good guy get to portray a villain for a bit.

ITS GREAT WHEN GOOD GUYS TURN BAD I LIKE IT IS COOL I THINK

It Depends On How It's Done.I Really Love The Idea Of The Most Unexpected Person Turned Out To Be Evil In The End !!!!

^ Yes!

I am writing a book that will have that happen in it
Also Jace turns evil in The Mortal Instruments and that is very awesome :)

Only if they have a good reason.