I encounter very bright lights occasionally.
They have never been more than a very temporary annoyance though. I've never been blinded, not had any damage to my eyes. Perhaps its the lenses on the £10 Bolle Screwfix safety specs I tend to wear? Highly recommended cheap cycling eyewear!
Whether cycling or driving, I can pick out cyclists much easier when they have blinking lights. Fixed lights are easily lost in urban traffic.
Flashers on a dark path are again only mildly annoying. Like me, I assume most I come across change between paths and traffic on their journey. I don't think its reasonable of me to insist they switch their lights every time. I'd rather they forgot to switch to fixed on a path than forgot to switch back to blink on a road, and stayed safer in traffic
I get much more annoyed by cyclists who don't know how to share space, who pass close without warning, or who buzz pedestrians. Still, i'd rather they were behaving like that on a bike than behind the wheel of a car.