A question for atheists (this is kind of long)?

Just to start off I am a theist, but I am not necessarily Christian.
Anyway, isn’t it safe to say that many modern atheists are atheists because they don’t believe in the Abrihamic Gods, yet you could believe in ghosts, spirits, whatever. However, if you don’t believe in anything spiritual or paranormal I have a HUGE question for you.

IS IT REALLY RATIONAL TO SAY THINGS THINGS DON’T EXIST SIMPLY BECAUSE SCIENCE HAS NOT DISCOVERED THEM?

Think about it. Let’s say we know about 0.5% of all knowledge in the universe, and that’s being generous because we don’t even fully understand our planet and our own bodies completely, so it’s probably about 0.0001% of all knowledge (probably still an overstatement). So, if we don’t even have the technology to permanently cure and prevent terminal diseases, and if we can’t even send a human to the edge of our solar system safely and get them back alive, then how can people honestly say " There is no such thing as ghosts, spirits, mythical creatures, ect."?

Think back to when the world was disconnected and fragmented. If you told someone who lived in an area uninhabited by lions that there was a giant cat with the beard and hair of a human (rough description of course), they could call you a liar. So isn’t it possible that ghosts, mythical beings, God, and even our own spirits live separately from us on a different dimensional plane that can not be accessed by our 3rd dimensional world view?

Yet all of these so called (often self proclaimed) "rational thinkers" seem to disregard the millions of testimonies, eye-witness encounters and say that that all of these millions, possibly billions, of people are delusional. If you were to really think rationally, you would know that this evidence suggests that there is something else out there that we have not discovered.

I understand that today if you say you believe in anything that isn’t common or is rarely physically seen by many people, then you are thought to be either crazy or less intelligent (which I think is depressing and kills creative thinking). However, is it REALLY rational to claim that because you yourself have never had a paranormal experience, that paranormal experiences are illusions or tricks?