When St. Thomas doubted the story his friends told him about the Resurrection, he offered up a standard: if he could stick his finger in the holes in Jesus, he would believe. Then, the Lord appeared and offered him the opportunity.
Many times when I deal with people who do not believe, or say they have doubts, I try to push them to describe a sign by which they would have enough proof. Some do, most don't.
That's because they are really not interested in believing. After all, if you really wanted to find the truth, then you would definitely have a sign in mind, or at least contemplate. But, some people like the ambiguity, because it excuses them from having to do anything different.
I call it 'militant agnosticism.' These are people who go out of their way not to believe, or to not know
We have all suffered from this from time to time. I know now that the less I know about the world, the better I sleep at night. But, that's largely because the more problems I hear about, the more I want to fix them, which is always a bad idea. Most problems work themselves out without my help.
But, I am responsible for the problems I cause, and so I must know the truths that immediately effect me, and none is so important as whether God exists or not. If God exists, then everything I do has a consequence. If He does not, then it is just about what I feel like doing versus whether I will get caught. These are profoundly different paradigms.
The person who refuses to know has contempt for the truth. It is different from doubt. The doubting man searches, but the contemptuous man avoids.
We can never be contemptuous, because in doing so we seal ourselves off from the possibility of finding the truth. Contempt is different from certainty and confidence, because it is possible to be confident in what one believes and yet, at the same time, appreciate other things for what they are and even desire to see truth in them.
For example, I can go to a Non-Orthodox church and appreciate the fact that it was built by people who earnestly seek God, even though I don't believe that how they are doing it is right. I can even appreciate the beauty and sincerity of a pagan temple, because these reveal the inner beauty of man seeking to express itself to the Divine, a beauty made by God with every human person.
Of course, I am intolerant of those beliefs which harm people, but I try my best (and often fail miserably) to not be contemptuous of those who do not believe as I do. I figure if I treat them better, perhaps they will become interested in what I have to say.
Then again, I have a church full of people on Sunday, and probably only a small fraction of them really take what I have to say seriously. That's OK, too: perhaps I am just full of hot air. Or, maybe they are not ready, but will be someday and I am laying the groundwork.
Doubts are good so long as we have a standard to end them. But, if we keep needing more and more evidence, but the goalposts keep moving, then what we are talking about is contempt for the truth.