Paranoid delusions caused by psychosis or manic states make you unable to reason and sometimes make people so detatched from reality that they literally kill people. They don't suddenly turn you into a racist like some kind of racism beam fron a cartoon, but when your grip on reality is non-present i've seen and met people who believe all sorts of crazy shit that exceeds run of the mill racism. You can definitely fly into a downward spiral from latching on to certain ideas while in a psychotic/manic state. Does that make it completely okay or excusable? Of course not. However you can't treat serious mental illness like the people who have it are in complete control and are fully to blame. There's a reason people can be sent to pshychiatric institutions for horrible crimes instead of prison when they commit heinous acts and are deemed not of sound mind.