Is it possible to allow sideloading and keep users safe?

Is it possible to let owners use their hardware as they wish, without having large companies control what they deem "safe"?

I'm not the user of my phone, I'm its owner.

Sure. But the societal losses of a vast amount of people getting scammed might in general be more important your individual wish for freedom to run anything you want on your device. I think there are important tradeoffs to be made, and that we have to acknowledge that many people in society less technically skilled might suffer from serious consequences in your proposed model of computation.

>But the societal losses of a vast amount of people getting scammed might in general be more important your individual wish for freedom to run anything you want on your device

The societal losses of a vast amount of people having no private, uncensored means of communication, which this is leading to, are orders of magnitude greater. The largest cause of early death in the past century was governments murdering their own citizens, and the more power governments have over their citizens, the easier it becomes for this to happen again.