To answer with more honesty, I think if someone has been working or dedicating his/her life to something it's pretty hard to just change right away. I don't doubt some priests may have started to doubt about Christianity or god existing, but since being a priest is the only way they have of earning something, it's very risky to just quit.
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you
