I had a teacher in high school who thought there was a chance (though he would admit it was small) this along with cell phone usage could be something with harmful effects that won't manifest for decades. He likened it cigarette smoking back before we knew about the cancer risks. Age restrictions were lower, you had doctor recommended brands, and smoking on airplanes was allowed. It was something everyone did and few people were concerned about the health implications until it was too late.
This wifi thing is probably a bunch of hogwash though.