For the supernatural, entering a human soul, opens it to new possibilities of both good and evil. From that point the road branches: one way leads to sanctity, humility; the other to spiritual pride, self righteousness, persecuting zeal.
And there is no way back to the mere humdrum virtues of the unawakened soul. If the Divine does not make us better, it will make us very much worse. Of all the bad men, religious bad men are the worst.