Defeatism and cynicism are very effective defense mechanisms, and the internet has made some people absolute experts at both.
All we can do is keep loudly pointing out how daft and counter-productive these behaviors are. Even if it's true, saying "x is useless" is also useless unless you propose to do y instead.
It's a real color (as real as colors can be, which is not very). It's not a spectral color, you won't find it on the rainbow. It's actually the result of your red and blue cones being activated together.