Is it possible to allow sideloading and keep users safe?

Yes, obviously yes. In the same way we teach people to operate cars safely and expect them to carry and utilise that knowledge. Does it work perfectly? Of course not, but at least we entertain the idea that if you crash your car into a wall because you’re not paying attention it might actually be your fault.

Computers are a critical aspect of work and life. While I’m a big proponent of making technology less of a requirement in day to day life—you shouldn’t need to own a smartphone and download an app to pay for parking or charge your car—but in cases where it is reasonable to expect someone to use a computer, it’s also reasonable to expect a baseline competency from the operator. To support that, we clearly need better computer education at all ages.

By all means, design with the user’s interests at front of mind and make doing the right thing easiest, but at some point you have to meet in the middle. We can’t reorient entire industry practices because some people refuse to read the words in front of them.

But this sounds an awful lot like trying to avoid changing the technology by changing human nature. And that's a fool's errand.

There are always going to be a significant percentage of users you're never going to reach when it comes to something like this. That means you can never say "...and now we can just trust people to use their devices wisely!"

Fundamentally, the issue with people clicking things isn't really a problem because it's new technology. It's a problem because they're people. People fall for scams all the time, and that doesn't change just because it's now "on a computer".

But that's exactly the issue. You won't prevent someone from wiring money to Nigeria by restricting what apps they can install on their phone while allowing the official bank app which supports wire transfers.

If someone is willing to press any sequence of buttons a scammer tells them to then the only way to prevent them from doing something at the behest of the scammer is to prevent them from doing it at all.

But that's hardly practical, because you're going to, what? Prevent anyone from transferring money even for legitimate reasons? Prevent people from reading their own email or DMs so they can't give a scammer access to sensitive ones?

The alternatives are educating people to not fall for scams, or completely disenfranchising them so that they're not authorized to make any choices for themselves. What madness can it be that we could choose the second one for ordinary adults?

Arguably they already do and the numbers wanting an open phone are relatively trivial and the market ends up the way it has.

I do these days, happily, and I speak as someone who owned a Neo Freerunner and an N900. My phone is far too important as a usable, stable device to want to fuck around treating it as an open platform any more.

The market is consolidated into Apple and Google and neither of them actually offers this. Taking away everyone's choices and then saying "look how few people are choosing the thing that isn't available" is a bit of a farce.

Nobody cared, so they went away.

I mean it seems like your argument is "nobody wants this thing that people keep getting mad that nobody offers". Obviously people want it; otherwise who are all of these people?