How would things be different if there were no such thing as transparent solids?

Answer 1

Answer 1:

No cameras or television. Possibly computers, though it would have been a harder leap, and answers would have to display on something besides glass or clear plastic.

Mass destruction in war would have been slowed down, as it would have been harder for planes to exist. Planes that did exist would have to be flown on instruments, and those could not have glass covers on them.

Cars would go much slower, as there'd be no way to avoid the wind. That might also decrease city sizes.

Telescopes and microscopes would not be possible. Which would be devastating to the medical field. We might still have all the plagues and diseases of the 19th century to deal with.

Though it would have been difficult for humans to see anything (since our eyes are made out of transparent material)

Answer 2:

Another way to look at it is that without transparency their is no viable form of communication in the long run... too much chaos, and no way for stable outcomes to evolve. (eg. cars that can't see where they are going - you may never get to where you want to get to - not that you would know where you where to go in the first place)