The most common argument used in defense of mass surveillance is ‘If you have nothing to hide, you have nothing to fear’. Try saying that to women in the US states where abortion has suddenly become illegal. Say it to investigative journalists in authoritarian countries. Saying ‘I have nothing to hide’ means you stop caring about anyone fighting for their freedom. And one day, you might be one of them.
What I do on the toilet isn’t secret. You’re still not allowed to watch.
People doing only legal activities still don’t want others to have access to their bank statements, messages, internet browser history, etc. I’m doing nothing illegal, but still no stranger is allowed to wander through my house.
Privacy isn’t a tool for criminals. It is a basic right for everyone. The argument of “having nothing to hide” misframes the argument completely. You don’t need to counter a strawman with logic. You don’t need to start from their assumed position and fight back from there. Correct their base fallacy in the first instance.