Why do legit opinions get down voted. When something silly (joke) is posted, or something off topic is posted, then down vote - but to use a down vote to simply

Why do legit opinions get down voted. When something silly (joke) is posted, or something off topic is posted, then down vote - but to use a down vote to simply silence an opinion is wrong. He is simply making a comparison the reported price of the disaster to the 9-11 war on terror (which he/she feels was an unnecessary war).