You can't put an apple on their mouth to stop them from uttering those words. It's Inevitable. They may not be in the position to say those words and they may not know the whole story, but you can't stop them because it is their Human Right (unless the opinion is defamatory). You owe them those opinions, same way as they owe you. All you can do is Bear it,Deal with it, and Tolerate it. Like some of our Folks do....
"In the practice of tolerance, one's enemy is the best teacher"-Jack Welch
"Human diversity makes tolerance more than a virtue; it makes it a requirement for survival."
"Tolerance can lead to learning something. "-Wayne Dyer