TBH ive only ever been blinded by hids in 2 circumstances.
1. On range rovers and the like, their headlights are WAY too high up and always shine in your eyes.
2. Cars with reflector headlights with HID's whacked in.
Modern cars with projectors that are properly aligned make no difference if you have HIDs or halogens to the oncoming motorist. Yes its illegal, technically, but so are alot of things in this country...
Are they necessary? no. Is that "upgraded" exhaust (which most likely falls fouls of noise limits) necessary, no, and thats illegal too, but nobody on here will bitch and moan about those will they.
Fact is HID's do improve safety, they arent techincally necessary and halogens do a good enough job, but i feel i can see further into the distance with HID's and mine are properly aligned so its not just that factor, its because the light is more blue on the spectrum and the human pupil doesnt contract as much when shown a blue light as it does a yellow one.
If they were that dangerous they would be against MOT laws. Yes, testers cant actually dismantle anything to see what bulbs your using, same if if you decide to use 100w halogen bulbs, which are also illegal, but turn on the lights, stick your head in front and you will see if theyre HID's or not very very easilly.