Interfering with licensed radar installations would seem to be a legitimate problem.
[1] http://www.ieee802.org/18/Meeting_documents/2007_Nov/WFA-DFS...
I realize they're probably terrible quality, and that they're really just Wi-Fi dongles with amplifiers tacked on, and that overly loud signal amplification destroys close range performance - but still, I'd been meaning to get a couple of these and see how good they are.
So
This 5MW one: https://www.ebay.com/itm/171907612288
And this 5.8MW one: https://www.ebay.com/itm/222605454974
And this 6MW one: https://www.ebay.com/itm/171907483813
Are all 2.4GHz.
And I probably shouldn't really use any of them then. :/
They would be legal for a point-to-point setup, since they achieve their high EIRP due to high antenna gain (as opposed to high output power). But also due to that high gain, they're not really useful for anything but point-to-point (think backhaul between buildings).
You could also use them legally and usefully as a client (pointed at an AP) if you turn the power down so that the EIRP is 4 W (36 dB). You'd still benefit from the high antenna gain in the receiving direction (though not in the transmitting direction, which includes TCP ACKs).
Moreover, there are plenty of radios on the market that transmit all kinds of noise on these channels that isn't WiFi (e.g. my neighbors had a baby monitor that I could tell when it was on by how shit my WiFi was at that moment, FPV drones somewhat frequently use this band with proprietary analog video transports, etc.) This is permitted because these channels are "unregulated" (or, more realistically, "regulated for unlicensed operation").
On top of that, the FCC's official statement on this very topic was that what they really care about is the amount of power being put into these channels, as some aftermarket router firmwares of varying repute would let you crank the output wattage above FCC regulations for these frequencies (<1W power to stay within unlicensed operation regulations for 2.4GHz), and apparently some in-market WiFi routers picked up those firmwares as a "supported" option (I think ASUS and Linksys were both named). Most of these routers have since patched themselves to stay regulation-safe.
So, go nuts, just stay below 30 dBm/1W from the transmitter in 2.4Ghz channels or prepare for a visit from the FCC. (You'll have to do your own research for 5GHz).