Stating this as a fact is wrong. At best you could say "merely egocentric bravado and the fear of being uncertain IMHO". It's not an established fact
I will try to explain how I view this variant of non-religion. I have come across it before and it works in both directions, though also differently as weird as it might seem. Now this is not IMHO, but it is not a judgment, because it applies to virtual humans. And as far as I can tell it applies to you, Joe W and me. We just deal with it differently.
So forget evidence for a moment. It works like this: Take 2 or more humans and find something where they with logic it appears, that one or more must be wrong. E.g. if there is a God or not. If that can be known or not. The list goes on. For all cases where this happens apparently as per objectivity because it is independent of the mind, it must be a contradiction. Well, it is not.
How? Because the reason for all behaviors are subjective and will works as subjective behaviors as long as it doesn't violate the objective part of reality. Let me explain. I believe in God and as long as my behavior that follows from that works in reality in general I can believe as I do. But that applies to all such behavior and here it is for some non-religious people. They subjectively in effect believe that reality is objective. They don't notice that this belief is subjective, because it subjectively works for them and they don't believe, that they have this belief. To them it is an objective fact. It is not.
They don't understand that reality as it works for us while we are here is an interconnected duality of the physical and spiritual.
Some people overdo the spiritual and try to do it as physical. That never works, but to believe that everything can be done as physical works, because the belief is spiritual. Now of course these non-religious people will admit to have opinions and the like. But that doesn't really count, because of reasons... Now these reasons are in effect not physical, but rather spiritual.
So here is why you should stay away from them, when it comes to the spiritual. They can't do it, because they deny that they do it. So you can't talk to them about it. Now in general in the context of, if it is about morality, ethics, the mental and psychological or politics you can sometimes do it and learn from them. But if you go spiritual on the hardcore non-religious people it won't work. So you can "mask" your examples and "cheat" if you want to stay neutral and still try to understand what they believe and sometimes know about the world as such or the physical part of reality. Some of them are good at that, the physical part as long it is physical.
But stay away for debates with them about what reality really is unless you want that.
Now notice something. I am a practical realist and I can spot a lot of cases, where something physical is claimed to be spiritual. I general don't comment on those cases, but you can ask if you like.
But I also know that my beliefs are in effect always mine and if you can do it differently, then there is no reason for you to ask.
Regards
Mikkel