There isn't much point to the inverse. You load pages, including all the stuff you don't want, then disallow it. Closing the barn door after the horse has bolted so to speak. You also have to remember to check every site you visit, which nobody is going to do consistently. With disallow by default, it is obvious you need to look because the site isn't working. While I was required to do this for work, I found myself doing it on my personal systems too, because things are in general more pleasant. A surprising amount of sites work just fine for the purposes of browsing, and many more just requiring one or two domains added to the whitelist. Often leaving out large amounts of crap from several ad servers and metrics collectors and video streaming I usually don't want to bother with and popup banners telling me to disable my adblocker and font tweaks because I'm obviously incapable of configuring my browser to be most usable to me and 'tagmanagers' which apparently do absolutely nothing and widget for forms I'm not interested in filling out. I've more than once found enabling JavaScript makes problematic pages worse.