Here's the thing with email. You can sign up for Protonmail ... but you've still got to use email to correspond with others. And in all likelihood many of those individuals will be on GMail or some other less-secure provider unless you're using Protonmail as an enterprise solution, in which case the ratio of "secured" vs. "unsecured" recipients would likely tilt towards secured.
Email is insecure, and most users don't even consider security when using it. I've seen my own social security numbers sent out via email. I've seen corporate card credit card numbers sent via emial. I've seen other confidential financial documents and a myriad of other things sent via email by people who didn't know or didn't care that the method of transmission isn't secure because frequently it's not their information at risk. In my experience, medical data is treated differently because there are laws around how it can be communicated and stored. Until there's regulation placed around other pieces of information, and those laws get enforced, I don't know that people will change how they use and abuse email.
This was probably the biggest unsolved issue I had when seeking out a new email provider.
"Switch to this other email provider" is not going to get much of a result from your gmail/outlook-using contacts (especially if money is involved), and wouldn't even solve this issue unless you convert absolutely everyone to, for example, Protonmail. "Hey man can you set up this thing called PGP?" is probably even worse unless your social circle is all technically minded already. Even in a group of "nerds that play video games", I'd be surprised if even half of the group even know what PGP is.
So long as we're stuck with email as we know it today, it really seems like there is just no bolt-on solution that can be used to "fix" it.
>And in all likelihood many of those individuals will be on GMail or some other less-secure provider unless you're using Protonmail as an enterprise solution
This is true of the marginal utility of the first and last element in a network effect. We might as well push for a paradigm where hosts have no access to data rather than, in 1950 say "Why should I join the internet, there are no other computers on it"
Email is insecure, and most users don't even consider security when using it. I've seen my own social security numbers sent out via email. I've seen corporate card credit card numbers sent via emial. I've seen other confidential financial documents and a myriad of other things sent via email by people who didn't know or didn't care that the method of transmission isn't secure because frequently it's not their information at risk. In my experience, medical data is treated differently because there are laws around how it can be communicated and stored. Until there's regulation placed around other pieces of information, and those laws get enforced, I don't know that people will change how they use and abuse email.