I don' think any pilots have been blinded (no retinal burning)- they are reporting seeing a bright green light, causing afterimages and temporary night vision problems (bad enough when trying to fly). You are correct, the power density over the area of the pupil is low for a 100mw laser. A 10W laser gets close to dangerous at that distance.
One safety factor with a visible laser is how much energy can you get into an eye before the eye reflexively blinks. A near-infrared laser, say 850 nm, is more dangerous than a red (633) or green (532) because you won't blink until lots of power gets in.
Even if the visible beam is spread out, it will look like a very bright light if you look into the beam. But, the spread out beam is easier to aim.
Beam divergence: There are two mechanisms that spread a beam. Up close, the beam spreads based on the optics used in the laser. In this distance, meters to hundreds of meters, the beam spreads at perhaps a milliradian or so, a very tight beam that makes lasers so useful.
There is a range at which the wave properties of light itself causes the beam to diverge, the wave wants to become spherical and the wave properties push the photons to the side. After this distance the beam spreads rapidly. This depends on the wavelength of the light and the beam diameter.
If you want to propagate a beam over a considerable distance, you first expand the beam then collimate it. A 1mm beam spreads much more than a 1cm beam does.
Thank you. The little knowledge I had of lasers was the coffee table science book variety. This site is so cool that we can educate as well as entertain.