There is a difference from reincarnation, and "reincarnating", particularly if you actually determine that the original person still exists and you are suppressing them.
And even among the situation where you are suppressing them, there is a difference between doing so willfully, and doing so while also trying to escalate it to a societal level to be done to others. The former is a understandably selfish choice of self preservation. The latter is maniacal and evil.
Personally if something happened to me like this, I would do the best I could with what I could, live on the best I could for them. However if there were any sign of the original person left(ie I didn't actually reincarnate), then it would only be right to return what is rightfully theirs if it could be done. Perhaps there is a path to share where we both could exist collaboratively.
I don't disagree that if most people found themselves in this situation they would likely choose themselves first.