Answer:
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
It can pierce the best armor and make swords crumble with a rub, yet for all its power It can't harm a wooden club.
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What is so fragile that saying its name breaks it?
Hard to catch, easy to hold. Can't be seen, unless it's cold.
What covers its face with its hands, speaks no language, yet most known what it's saying?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?