From C. Stephen Layman, "Faith Has Its Reasons," in God and the Philosophers (Thomas Morris, ed.):
People often think it significant to assert that "God's existence can't be proved." A proof, I suppose, is something that will convince anyone who is intelligent enough to understand it. If so, very little of interest regarding major philosophical issues can be proved. This goes for issues in metaphysics, morality, political philosophy, and aesthetics. All or nearly all of the major positions under these headings are highly controversial. There are brilliant people on either side of the interesting fences. So, if we demand proofs in philosophy, we will wind up as skeptics on all or nearly all of the important issues. Surely that is not the way of wisdom. I often ask my students to imagine themselves giving an antislavery speech to a group of slave owners. What are the chances of convincing the audience? Slim to none. Surely, then, it is possible to have good arguments for a view even though these arguments are not recognized as such by groups of people who do not share our convictions.