The corollary is that you have to know what a
balrog looks like.
Elves know,
Aragorn knows, in any reasonable world
Dwarves know.
Hobbits...they dont know.
But, Aragorn did not know what a Balrog looked like as shown by his statement to
Celeborn: "An
evil of the Ancient World it seemed, such as I have never seen before. It was both a shadow and a flame, strong and terrible." Also, clearly the dwarves did not know what a Balrog was.
Figger that its the only thing that can accomplish that deed--destroy a
Dwarf City. Say...maybe it aint. THEN, being a nosy neighbor, I want to find out what did destroy the Dwarf City.
But, as you say maybe there are various things that can destroy a dwarve city. Since this thing,
Durin's Bane, shows absolutely no interest in leaving its conquered underground city, in fact, the evidence is that it is some sort of subterranean monster native to the deep underground that the dwarves were foolish enough to disturb, why go looking for trouble by investigating it. Remember this is a world of magic with various terrible things in it. If there is a terror that shows no interest in coming out to you, why go in after it. Or maybe, as Aragil suggested, the elves did send in scouts and none returned. How many do you send and lose? At what point do your scouts say, "Hey King Celeborn! You are so interested you go look!"
Not believe the propaganda that ALL
BALROGS ARE DEAD (
Maia, notwithstanding) and put 2+2=4. If it wasnt a Balrog, it was the moral equivalent of a Balrog.
But you don't have 2 + 2. You have 0 + 0 = 0. Whatever is in
Moria is big, nasty and foul-tempered. I would leave it alone.
I am afraid,
Harad, you are
the one doing all the whistling.