For every sicko who's trading child porn there's dozens, if not hundreds, more who're trying to escape an abusive partner, leaving gangs, getting away from sexual slavery, or whistleblowing on government or companies breaching the law.
Additionally, should the millions of us engaged in perfectly legitimate activities have a dossier created on our lives just in case? Imagine what could happen to that information, you could be facing secret blacklists like the UK.
If Apple create this ability its use will extend past the immediate issue and affect people who genuinely need this security. In the digital world, as Apple said, you cannot destroy something or lock it away once it's used.