Agreed - see below.
Where it is written that you have no right to privacy in an airport? TSA (and its international counterparts) has limited authority to search people and property beyond what would be allowed in other contexts. They can require that I submit my bag to an x-ray, and they can open the bag (or better, ask that I open it) to look at my papers to ensure that they are indeed papers or that the laptop is a laptop.

They do not have the authority to read the papers and copy down information from them (company data, research results, account details) or browse the laptop to see what my taste in music is like. The contents of my papers and laptops are still private to me.

Similarly they have the authority to search my person to the extent necessary to determine that I am not a threat to the aircraft. They do not have the authority to require that I strip naked in the concourse, or ask questions about my health, food preferences or personal habits.

And that's only at the checkpoint, not the entire airport. Airport staff can't demand to know my salary or ask whether I drink alcohol simply because "there's no right to privacy in an airport".
And they used to say lots of other things were "incredibly safe" and they turned out to be "incredibly safe."
The MMW scanner uses radio technology which is directly comparable to numerous other technologies which have been in very widespread use for decades and which are not considered harmful. The power levels can be directly compared to, for example, a cell phone or the radar sensors that open doors at the grocery store - the MMW is many orders of magnitude lower. (Yes, this accounts for the fact that you're close to it and it's "focusing" the energy at you and everything else - even with all that it's orders of magnitude less radio energy than your cell phone.)

As Allie said above, if the MMW is dangerous, then cell phones and other radio systems would be causing people to immediately drop dead all over the place.

I think grey carpets are incredibly safe. But I doubt that the grey carpet at SYD security checkpoints has ever been properly tested to see if it causes cancer. "Safety" doesn't work like that - it works on the basis that carpets in general, and grey carpets in other contexts, have never been implicated in cancer, so there is no need to test the grey carpet at the checkpoint.