WiFi transmitters are very low power devices with a range of a couple hundred feet. I would suggest that the paranoids first focus their attention on the several dozen television and radio signals that are presently passing through their bodies and have been for as long as they've been alive, and when they've worried sufficiently about them, think about all the electromagnetic radiation from space that has been passing through humans for as long as we've been around as a species.

Now if they wanted to ban cellphones in public places, THAT would be a great idea!   :-)