While I understand that it is rude to challenge a specific persons beliefs, I feel that it is unfairly so. If your grandma found out I was an atheist and said, "Young man, you really ought to find god." It would not be seen as being rude on the same level as me telling her that her system of worship is deeply flawed and based on nonsense.

Yet, I understand why this is; there is a very good reason for this disparity in perceived rudeness. One person is basing their assessment on sound reasoning, while the other is ignorant and delusional. Calling a retard stupid is rude; a retard calling you stupid is almost endearing.