While this is far more elaborate, I agree it's the best approach if the other person is willing to have a discussion.

You may sprinkle it with actual examples of what's happening in China with their point system: not getting bus tickets or loan grants or whatever because you not even mentioned something critical somewhere but are associated with someone how did.

They may say it's unrealistic but 30 years ago Eastern Germany was the same. They just lacked the tech and needed to recruit regular people as spies.

This is a good point and got me thinking of something that would be a better example. I understand the point that it's because they don't really care about some corporation without a face collecting their info, which is different from you who they personally know asking them to unlock their phone and give it to you.

Maybe a good example would be their baby monitor or home camera? Let them know that anyone on the internet can tap into their camera feed because those companies don't lock them down. Not that anyone is looking at it, but anyone could if they wanted to. Would that be a more convincing argument to ask if they are fine with that since they have nothing to hide?

Finally someone who gets it. Imo, the comments asking those people to hand over bank details and similar stuff can harm the argument. I mean, if someone told me that, I'd just say I do that every time I go to the bank. Or my bank has those details and they're made up of people like me. It won't really convince me that privacy is important since most of them probably have never experienced getting their accounts hacked.

they have nothing to hide from those with access to their data (governments/corporations).

That is only a good point until you remind them that the government/corporations aren't just entities but also consist of people, any of which could end up being their neighbor tomorrow, hold their next job interview, be their next potential tinder match, etc.

Of course the rest of what you wrote is true too, but I really felt the need to point this out.

To give an example: I'm in data science. As part of a contract work I had access to a csv dump of a database of addresses of all people who ordered campaign material for a specific political campaign. I could have easily sated my own curiosity and checked who in my near vacinity is in that list, as well as the exact amounts that they ordered and some other notes about them. Suddenly it wouldn't just be some corporation anymore but their neighbor.

Those corporations and governements have people employed who can have (and usually do have) access to the data. Intentional or unintentional. So would they still be comfortable knowing that I'm able to lookup their data? That's what the personal questions are about.
If the government still had personal interactions with a clerk at a desk, would they still be comfortable sharing everything they do now?