Well, the facts mentioned in the post just confirms my judgment why MooTools/Prototype are bad: monkey-patching existing objects and polluting global namespace like no tomorrow, all in the name of object-orientation in a perfectly capable language that's prototype based and functional.

If you can't be bothered to author your code using only ONE JavaScript library, then yes, name space "pollution" is not very friendly. But if you write all your code using one framework, then the name space is yours to use, which to me is not pollution. It's only a pain when you want to use several frameworks, and the only reason I can imagine to to do that is to use plugins from more than one. That's laziness if you ask me; rather than ask your users to download two libraries, you should author your own version for your framework of choice.

Sorry, but we do want to use actual useful objects (including built-in types) no matter what you'd say.

It's viable, it's useful, it's done, it works.

That's a fine reason, as long as you don't care about being friendly for integration/customization/embedding with external sources.

Should I?