More like anything electronic is more apt to fail than fixed sights!
How often do the electronics in your car fail you? How about your tv? prone to failure? Whens the last time your radio quit...
Although these things certainly can happen and eventually will if you dont change them every so many years they tend to work for a vast majority of the population...
Fear of a laser not working at a critical momen is IMHO foolishness because in the end the bullets going where the sights are if the laser fails...
I suppose this forum is filled with people who never use cruise control because it might fail....