'War of the Worlds'
Let's start out by dabbling in the social sciences here. In the 2005 version of "War of the Worlds," Earth is a world in which cities apparently don't issue building permits, and there are no busybody neighbors hovering around to see who's next door digging a hole for a new "pool." Either that, or somebody actually managed to get permission legitimately to bury alien killing machines all over the place. Another potential argument is that the film's alien murder machines predate human settlements, which would just mean that we're really awful at evaluating real estate expansion plans. Granted, that's closer to stupidity than science.
But bad science there is, the biggest share of it committed by the invading aliens. They like to munch on a particular plant-ish substance, but that plant apparently needs human blood to nourish it. Important question: What type of Miracle-Gro were they using before they stumbled across Earth?
Let's just put the idea that an alien life-form could somehow require human blood to survive to the side for a minute. The aliens were obviously smart enough to figure out what they inexplicably needed. Yet, they somehow simultaneously overlooked the heady, bursting-with-bacteria brew they eventually fell victim to.