When you give users a clear, informed, singular choice that would be sticky across their entire web/app experience, the choice in itself essentially becomes obsolete. Since pretty much nobody opts-in.
You saw the effect with Apple's new "do you want to be tracked" permission, which has a disastrous impact on Facebook. Consider that this is still a per-app permission, imagine the impact when its a single permission across all apps.
As users we may say "good" and "this is what we want", but I don't think we can truly oversee what impact that would have.
