vitiate
verb
°to spoil, make faulty; to reduce the value, quality, or effectiveness of something.
"1997: ‘Mr Rose,’ says the Physician, ‘this man was brought to us from Russia. Precisely such a case of vitiated judgment as I describe at length in my Treatise on Madness. Mayhap you have read it?’ — Andrew Miller, Ingenious Pain"
°to debase or morally corrupt.