We are using a strictly point to point collimated beam that is expected to meet nothing but clear air. It shuts down if/when any transient object is about to enter the beam path.

Also, don't forget that the important figure you should be looking at is power density rather than total power

You also claimed it's unaffected by rain.

Which is it?

Rain will trip the laser screen, as will fog.

Ergo, this will only work in clear air. Rain and fog will shut it down.