You can already write a desktop app to do all that malware stuff. Why give the phones and tablets special treatment?
Personally I like the iPhone and the App Store for the reason that it does go through some basic checks.
But as a dev, sometimes I just want to run my own shit on my own phone without hassle. (Yes I know there is dev mode. I don’t want to constantly run my main phone in dev mode just so I can run my own apps.)