Then I guess people should stop the spread of information on this site concerning the nitrogen cycle, medications, ect ect, because I doubt ANYONE here except for a select few have actually checked out Nitrfying bacteria under a microscope.. and I HIGHLY doubt anyone on this board, or any fish hobby board for that matter, has scientifically engineered their very own antibacterial medication....
Using your Logic, History teachers should quite their jobs. How do we know Rome crushed Carthage? How do we know Saladin recaptured jerusalem? there are no Eye witness's alive... We have only documented information... How can we trust that? We didnt experience it!! that means, we have NO knowledge about it!!! NOTHING VALID ATLEAST!!!!
Knowledge can be acquired 2 ways.
Reading and or learning from others
and/or
experiencing.
So, your point is moot.