Black holes is not the absense of light, Nor it is nothing.
A black hole is a mass in space which light ( or anything else) cannot escape from.
Yes, noone can see a black hole since "sight" is actually the reflection of light information( and color) that is take in by our eyes. Since BH absorbs light past the even horizon, one cannot see it ( since no light can bounce back into our eyes).
These guys are the definition of idiots. If there was a black hole that close to earth, we would be dead before we noticed anything was wrong. (crosses fingers for stability for the large hadron collider in europe)