Your webcam isn't religious
Well, it depends. Maybe all matter possesses a little bit of a spirit. In that case, it is. So it depends on who you ask.
You say prove there is a spirit. You claim there is no way to do so. I deny that. It is perfectly possible to prove or disprove (depending on whether there really is). The problem is that we don't have the needed physics yet. 2000 years ago, you could have asked me to prove that you didn't have a whole mess of little wriggly squishy things shoved together to create your body, and I wouldn't have been able to. By your definition of "know", we now know that you are composed of a vast number of cells, each one a living creature that eats, metabolizes, grows, reproduces, and dies. In essence, you are actually a composition of many smaller creatures who live and cooperate with eachother to support the community that we see as your body. All you are is the sum total of them.
But 2000 years ago, that would have seemed even more ridiculous than saying that you are insane and only imagine having this conversation with me, or that I have a spirit, or maybe eight trillion spirits that merge together in a kind of government to create the entity known as Pizzasgood.
With the rate modern science has been progressing, who knows what we will prove or disprove in the next 2000 years (if we don't kill ourselves or partake in a religious ending first).
I'm not trying to prove spirits exist, just to explain why it isn't ridiculous to believe such a thing.