How can anyone possibly think this is a good idea?
This is such a bad decision that it almost disappoints me more than Ubuntu's relentless push of the badly broken and poorly designed Snap ecosystem.
Why should it not? For the most part this flag seems to be working. And it improves security. Windows can't do something like that for most of the software targeting it because it's all in binary form. For the software available through the default Ubuntu repos, source is available, so Ubuntu can offer this.