ANSWER:

He should not waste his great rewards of forgiveness and giving other the benefit of the doubt just like that.

Allah loves those who forgive and pardon others for His sake. 

There is a brother who used to always make excuses for people in his community even when they made major mistakes and hurt him. Then, about a week ago, he had enough and said it was his mistake to ever think well of them and that by default from now on he will assume anyone he sees in his community is evil until proven otherwise. What advice do you have for this brother?