While sincerity is usually mentioned among life's virtues, we must remember that it is possible to be sincerely wrong.
People often are.
A person may be sincere in one's persecution of other people, one's bigotry, one's aggressive attacks like what is happening in the Middle East these days, but that sincerity does not remove the evil of it. Paul was sincere in persecuting the Christians, and later sincerely conceded how wrong he was. Persons are sincere when they make bad investments, but their sincerity doesn't prevent them from losing sometimes the savings of a lifetime. We must remember that it is not only necessary to be sincere, it is necessary to be right. Faith in a wrong cause, work for an unworthy one, belief even sincere belief in error and untruth, is a tragedy.