Faith and Doubt are two sides of the same coin and this applies to more than religion. There are many beliefs systems such as economic, political, social, and personal. You may have faith in democracy or in capitalism and you may at the same time have doubts about aspects of either. Doubts are those little nagging questions that have never been fully answered for us.
Doubts actually helps us strengthen our belief systems because being able to question what we believe either gives us a stronger understanding or causes us to change to a better system. What may be better for us may not be appreciated by those around us. We have to be able to answer our own doubts and questions in order to articulate our concepts to other fellow travelers.
In our republic we are always questioning our leaders and that is a good thing. In dictatorships questions are not allowed and that leads to oppression and pain. Today we have a variety of political groups that raise plenty of doubts about their opponents and that can be good but we also need to evaluate their bias and question their version of the truth.