K came to destroy humanity so why take human form and talk about it? If he wasn't sure what he should do then it would make sense to first have a chat about it before making a final decision, but he was resolute from the beginning. It was only after meeting some nice humans he changed his mind. There is no logic in the story.
Not only that, he got shot by some dumbass sniper/cop who *beep* his pants and couldn't hold the damn fire. Seriously, some alien life form is coming out of a big ball of shiny light and the first thing you do is shoot it? At that moment they could just wipe the earth of retards like that cop and leave the smart ones, sorting out would be an easy task.
The increase in human knowledge is the cause of the decline of religions.
That's exactly what would happen. The gun nuts that carry to Denny's would be the first to run out into the parking lot and start shooting at the "What duh hell is dat???!!!" as it prepared to land or scan.