I get relying on 3rd party libraries, but not hosting them yourself and just hoping that the current host never gets sold/owned/etc? That sounds insane to me...
Sounds pretty insane to me too, but I think it is valuable to let people do insane things more securely, as I don't think security concerns are generally a very big deterrent in software development (unfortunately).
And those 3rd party libs can dynamically load other files via script tags. The first level does not even have to change for dynamically loaded scripts to change.