Full legal protection is to things that are legal. For example a contract between two willing, free and sane adults is not necessarily a legal contract. If the contract is for an illegal act, why then the contract is void. Legally unenforceable.
If the meeting, though private, involved the corruption of minors -- an illegal act -- why then a private party may well be protected from prosecution for taping same. The Bill of Rights prevents the police from doing so without cause and warrant, but does not apply to a private party.