John Stuart Mill gave his answer on p. 938 of the Liberty Fund edition of his Principles of Political Economy, in volume 3 of his collected works:
“[T]he onus of making out a case always lies on the defenders of legal prohibitions.”
The modern legal scholar Randy Barnett calls this the presumption of liberty. People are presumed to be free to act. If a third party wants to intervene, the burden is on them to prove why they should be allowed to.