Fear believes, courage doubts.(from his Lecture on Ghosts - see this collection in Project Gutenberg for the full text.)
I know that this can be taken in different ways by different people, so I offer more commentary than I usually do with quotations.
For those of you whose first impulse is to be insulted, I encourage you to try to step back and see the sense in which it is a valuable sentiment. Note that it does not mean that all belief is born of fear, nor all doubt of courage; it just means that fear is a great motivator of ill-founded belief, and courage an important foundation for honest doubt.
For those of you whose first impulse is to feel smug - that this is a condemnation of someone else - I encourage you to think again. Do you apply doubt to all of your beliefs, or are some "special" in one way or another?
Ingersoll's quote - from a discussion of witch-hunts and superstitious hysteria - is a warning to us all. It is a statement about human nature, not just about one type of worldview.