If someone who ought to do better falls for the 'if you have nothing to hide' nonsense...

[marjaerwin]

You could ask them to imagine having innocent things to hide, such as being trans or lesbian or bi or gay and having to hide this from homophobic parents and/or bosses, or being a survivor and having to hide this from anyone who might be a compulsive victim-blamer, or being an activist [though all too many people think concern for humanity is treachery to any given country].