[jodrellblank]

It's pretty likely that the moment sideloading is "available but off by default" is the moment phishing messages take off seriously. "Just go to settings, then enable sideloading!". Most people won't know what it means, but will use it if told to.

That's not something I can cite peer reviewed evidence for, but from the number of people with unwanted toolbars and junkware on desktops, it seems likely.

So I disagree that it has "nothing to do with a good experience for users".

the walled garden approach is frighteningly dangerous for computing in general.

It has made something widely regarded as the best non-technical computing experience of the decade. It's not 'frighteningly dangerous' while there are still lots of ways to get computation you want done, done. (Albeit not as slickly).

[mikeash]

Sideloaded apps could still be sandboxed. It is the sandboxing which helps against malware, not the App Store approval process (which is not at all thorough and not equipped to detect malware at all).