That and you can't use defamation to instigate a fishing trip. I.e I can't make the claim you raped someone and then as my defense get a warrant for all of your stuff to look for evidence of sexual misconduct after the fact. Making a defamatory claim is not itself probably cause for search and seizure. If it were, I'd say it about politicians a lot more often.If even that. User information shouldn't be relevant discovery material, and they may be forbidden to seek it or punished if they seek it.