because it's very hard to study this stuff
It's 2016 and we're still claiming things that are very easy to study are actually very difficult.
In the EU we got vaping (gas chromatography and, y'know, mountains of research into carcinogens/poisins/toxins in vitro and in vivo), and apparently in the US they got WiFi because it's not like anything like MRI or basic cognitive testing of any sort was ever invented or anything.
If WiFi was damaging to brains (or in fact the opposite of reality where kids are getting smarter because despite falling funding pretty much globally we're as a species getting better at education) it'd be really obvious in the available data.
It's fine being against things that are essentially good but at least present a shred of evidence.