Hm. Sure, some people just point to how the same thing happened with GSM, 2G, 3G, 4G, WiFi... but that's just a fallacy, because we also know that gamma rays, X-rays and UV are harmful, so deductively there must be some grey zone between 3G and hard gamma rays. Since we can't simply infer the health effects with certainty from first principles (let's say from physics/chemistry) we should demand relevant data.
But we have a lot of data (even if not as an enormous pile as about WiFi), and we know that so far the evidence points to no unexpected effects. There are interesting avenues of inquiry about
the effects of 50-70 GHz on biology (heating of insects, interference with bacterial growth), of course those effects are a lot smaller than what we already do from air pollution to manufacturing an dumping lot of chemicals everywhere, heating our cities, and so on.
Between Gamma rays and 3G is UV. Between UV and 3G is visible light. Between visible light and 3G is IR, one of which is the heat human bodies give off. Do warm blooded animals cause cancer? Because they're still a far higher frequency than 3G and the wattage of a human at rest is 100W which is roughly equivalent.
Do hugs cause cancer? If yes, then we can start narrowing it down to 3G/5G more after that. But by that stage I think we're doomed as a species anyway.
No, we can quite safely say that visible light also does not cause cancer, seeing as how we're bathed in it daily.
So any proposed grey area would in fact have to be a total surprise outlier, where EM far less energetic then visible light tripped over some biological weak spot.
Visible light is between 3G and gamma rays. Gama rays are dangerous because they can yank electrons out of atoms and thus change their chemical makeup.
But we have a lot of data (even if not as an enormous pile as about WiFi), and we know that so far the evidence points to no unexpected effects. There are interesting avenues of inquiry about the effects of 50-70 GHz on biology (heating of insects, interference with bacterial growth), of course those effects are a lot smaller than what we already do from air pollution to manufacturing an dumping lot of chemicals everywhere, heating our cities, and so on.