He had to come to grips with the reality of his own soul; he wanted to believe or pretend that he was not the kind of bigot that his friend had told him that he was. Peter felt that he was morally superior, not inferior, to others. He did not hate anybody, he did not have a coursing rage going through his body that dictated being mean or being rude to others, and he did not deliberately discriminate.
Yes, there was a part of him that wondered - aren't friends there to show each other their faults and weaknesses? Perhaps he believed he had been covered in a type of righteousness that made him immune from finding fault and creating or sustaining friction to those around him. But perhaps he was wrong. Perhaps, in actuality,he lay bare, exposed, unhinged, maybe even uncovered and he didn't realize it. Maybe the reason we let friends into our hearts is because we, unwittingly, prove how diaphanous our heart really is - and how our friends can really perceive who we are.
And after all, they say that it is not the kisses of the enemy we need ... but the wounds of the friend is what is necessary to proceed to the next level of humane gentleness.