What is the significance of calling something a social construction?

[Slander and/or Libel]

Saying that something is a social construct is a way of saying it's not an immutable truth. That doesn't mean it can/should be discarded (lots of stuff that people made up is good and worth hanging onto), but it does mean that if we realize it's made up, we can stop treating it with undue reverence and evaluate it on its merits, rather than as received wisdom.