So, why believe there is a God if we cannot know with any reasonable degree of certainty that there is one? That is the question.
There are reasons to believe. Some find them compelling. Some don't. One of the least valued and most overlooked is the sheer fact that in American society most of us have been raised to believe that there is a God. Even today, many long decades after Darwin, the vast majority of Americans believe there is a God. The vast majority of Americans, even those who are not Christians, value the person of Jesus of Nazareth. He is, as more than one scholar has pointed out, an American icon. For those not inclined to engage in doubtful reflection, the very fact that they were raised to believe in God is a compelling reason for doing so.
There is another consideration. Our socially-based belief in God is not "merely" heedless and superficial. While that belief says nothing about whether or not an objective reality called God does exist, it suggests a good deal of social reflection and, perhaps, even some wisdom. Our socially bred belief in God, for example, is rooted in the immigrant experience of several peoples and groups fleeing religious persecution. Belief was important enough to them for them to remove themselves to North America rather than give up that belief. Our belief in God is also rooted in the revivalist movements of colonial times, which eventually bred liberal social justice movements as well as conservative evangelistic movements.
The point is that our American social commitment to theism cuts both ways. Yes, it does suggest a superficiality and a herd mentality. It also embodies, however, the experiences, deep thoughts, and even wisdom of our society as well. For tens of millions of Americans, those experiences, thoughts, and that wisdom is compelling. They believe, whether deeply or superficially, that there is a God.