Some War of the Worlds readers argue that the Martians are really dumb for coming to an alien planet (Earth) without minimal safety requirements. Come on, Martians, where are your space suits? Despite that big oversight, most of the folly in this book is committed by humans. People watched Mars, but never figured out what the flashes of light meant. Humans rush out to see the Martian cylinder and then trample each other when they run away. People try to make contact with the Martians, never thinking they might be dangerous. The examples go on and on. In The War of the Worlds, folly (and its close relative, pride) is really one of the main reasons why the Martians kick human butt so badly.
Although folly is a dangerous human trait, Wells shows that the only way to not be foolish is to experience some kind of hardship or tragedy.
In The War of the Worlds, Wells marks all the foolish characters as foolish because the readers could easily agree with them.