There is a difference though. All we need to do to prove leprechaun doesn't exist is simply turn this world right over, every single square inch, and we'll be able to prove that it doesn't exist on earth.
You can't do that with spiritual beings/person/whoever... with that said, what I believe is "Keep an open mind and don't disrespect what you don't know."
Apparently you've never heard of space leprechauns. Besides, everyone knows leprechauns can make themselves invisible.