Everything is a double-edged sword. Even a single-edge sword is a double-edged sword.
It's not really a paradox, though, because "being a double-edged sword" is a comparison that's being made with regards to the decision of using that particular single-edge sword.
And "being a single-edge sword" here is a technical description of the physical object.
But that quote is something worth writing down somewhere.
It's from a Louis C.K. routine.