> Compare this with old-fashioned CBC+HMAC (applied in the correct EtM manner), in which you can arbitrarily misuse the IV (for example you can forget to apply it completely) and the worst that can happen is that you drop back to ECB mode, which isn't perfect but still a long way from the total failure that you get with GCM.

It is not. As Dan Boneh stresses in his cryptography course, a cryptosystem is either secure or “terribly, terribly, insecure”.