Well, thats an answer far deeper than I expected...

If it were unequivocally true that properly playing an insane character made the person themself insane, then I would already be in an asylum...
Of course none of the insanities my characters have featured in the past have been to quite the level you use as an example here, but they have, nonetheless, been insanity.

While I cant speak for others, I know that for me RP is a medium to explore (among other things) actions that I would personally never do, or sometimes even find abhorrent in the extreme and actively oppose.

Philisophical discussion aside...

I am now presented with the choice....
Do I play Cerria, or do I play Cerria reincarnate?
Any idea how long the plot will go for on an in-world basis? If it goes long enough I could do both...