Even empirical truth has a remarkable degree of social construction. Consider the notion of "force", as empirical as it gets. But then you look at relativity or even just centrifugal force. Scientific revolutions consist of reinterpreting objective facts.

It's not just "nothing is real", which is just intellectual laziness. It's noting that we always interpret the world; we can't avoid it. Ordinary interactions usually arrive at similar interpretations, but people have a remarkable way of being influenced in that judgment. And sometimes that can lead to some really bad outcomes. It's important to recognize that the potential is always there even in things that seem obvious.