The physics of the 2.4Ghz frequency means it excites water molecules... of which our bodies made of up to 70 percent. The brain and nervous system is mostly water. 2.4Ghz is also fairly decent at penetrating most materials. Therefore it's only a matter of how much power is emitted and absorbed at that frequency. If you are comfortable with these facts then you have nothing to be concerned about.
However, I choose to have 2.4Ghz Wifi running as low in power as I can get away with no matter what device is emitting it... cell phone, wireless router, laptop, cell tower, etc.. Also... This is not secret information, speculative or debatable information about 2.4Ghz. It's been well known for a very long time and you can read about it in any science related book and all over the internet.
Physics? Anyone who did not take physics in school? How about cosmic rays? How about X-ray, Cat scan, MRI at hospitals? How about high tension lines feeding power to our home? We live in it. So many things are beyond our control.