Lots of angles here. For one thing, consider, like a Humean skeptic, small things. You believe if you hit a billiards ball with another, it will roll away at a certain vector. How might we justify this belief? You might say, "well I have seen billiard balls interact before, and this prediction is consistent with my past experiences, I have no reason to believe otherwise." Hume would say: "the belief itself that you can predict a phenomena based on prior analogous observations cannot be justified alone by those observations." That is, there is nothing in your experience alone that proves that things that act one way in the past will continue to act that way in the future, there is something like belief there.
But you are probably smarter than that. You would say, "well the study of physics shows that we can generalize the behavior of bodies in space such that we can predict their behavior. And look! We can make planes and computers and such with these generalized rules, so they must be real." But what fundamentally has changed here? Not only is it ultimately the same act of belief, but now you are at best 1 step removed from actual experience. Not only are you putting some belief into the consistency of the universe, you are putting it into a giant infrastructure of research and peer review and state-interest and grants that you can't possibly be personally a part of entirely. You have in fact contracted out your empirical life to others!
Because it is "better" or "worse" as a story, does not change the fundamental act of belief. Hume, I believe (its been a long time), would say this kind of believing is a habit, which makes sense to me.
To get even crazier, consider even perception itself, as Husserl did. You are looking at a table in your room, you can't see the other side of the table, but you "know" its there. But what do you really know? You know that perception itself tends to present a "world" with certain characteristics like extension, where moving around an object will present different parts of it. But that perception "shows" you a world like this does not justify the world itself, only the characteristics and tendencies of your perception.
This is what I mean in principle, perhaps we "know more" but we are certainly not "smarter" than religious people of the past. We just have longer stories for things. Stories that are sometimes, but not always, more fruitful.
And a related but different angle: I think even secular/atheist/agnostic people who aren't even necessarily militant weirdos like Dawkins/Harris unconsciously must contextualize themselves and their life in a world of belief. Trivially, you not believing in god is not an absence of delusion or whatever, but necessarily a belief. You go about the world and live your life based on unconscious assumptions that there is fundamentally a ground you are standing on, whether you are a philosopher or not.
