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.
“I don’t have anything to hide because I think I’ve done something wrong: I have something to hide because I question your judgement and motives.”
They’re fine giving you their info because they trust you. The problem is when the person seeking that information is untrustworthy – and some shithead(s) making their way into a company or government isn’t just possible, it’s likely.
Tell them to give all their sensitive personal information to someone that hates them. Credit card numbers, political beliefs, nudes, sexual preferences/fetishes, etc.