After quite a lot of thought and some attention to some of the issues that surround web apps that use hashbang URLs I’ve come to conclusion that it most definitely is about the hashbangs. This technique, on its own, is destructive to the web. The implementation is inappropriate, even as a temporary measure or as a downgrade experience.

I agree. Hashbang approach is a very fragile attempt to improve experience in an app-centric world. Suddenly you are at the mercy of the JavaScript developer whose implementation approach could be wrong or could easily break or overridden with simple embedded JavaScript or hacks. See some great discussion here, Breaking the Web with hash-bangs.