X-Men: 10 Things Everyone Gets Wrong About The Phoenix
6. The Phoenix Drives People Insane
Now, you'd be forgiven for thinking that the Phoenix Force has a tendency to drive people insane with power, but in actuality that isn't speaking the case.
As part of its role as the embodiment of life and passion itself, Phoenix doesn't just fix and restore life, but actually can occasionally destroy it, as part of the 'Judgement of the Phoenix' it will sometimes burn away what is 'obsolete'.
So while the Phoenix has gone mad, it's not because of the Phoenix Force and its power itself. Rather, the Phoenix Force went dark in the Dark Phoenix Saga because a villainous telepathic mutant named Mastermind manipulated it and drove it mad. And when the Phoenix was forcibly split across five mutants not intended to be it's hosts in Avengers vs. X-Men, those hosts arguably went mad with the power due to the fact they were never meant to be hosts in the first place.
So you can blame Captain America and Iron Man for that one.