Is it appropriate to ask an imam about his "creed/belief" to determine if one should follow him in congregational prayer?
I think asking the Imam his creed before taking part in the congregational prayer is an act that cannot be condoned. Difference of opinion should not lead us to that kind of dissention.We should try to talk such people out of this attitude wisely and educate people to avoid extremism. Dialogue would better solve the matter and create an atmosphere of agreement and acceptance among the different sects of the Muslims. We should focus on the unity of goal (of success in the Hereafter) rather than fighting on minor differences.