Why? Who is forcing YOU to sideload?
There's no reason why the default couldn't be status quo and you'd only opt in into sideloading, this way the users who want the walled garden still get it and the users who want to sideload can optionally opt into that.
Why is it always an either/or?
As for Android, I'm pretty confident in saying that F-Droid, which is a 3rd party store, is generally safer than even the Play Store.
Android's problem is the lax review of apps even on the Play Store, lack of updates soon after purchase etc. Most users on Android don't even have sideloading enabled, that's not a huge vector.