A city could not continue to govern such a large area. And maybe it shouldn't. Human nature and all that "rot." IMO, society is stronger when individuals take on responsibility, instead of vesting it in human "governors."
You can talk about character and values and the wrong type of christianity all you want. For my money they could not govern developing regions like Germany, England, Turkey,Spain and France, and most of central eastern Europe from Rome. I stated the military and political reasons why the empire fell. Simply, you cannot split the empire into three sections and say look we're still Rome. And hiring a bunch of Germans to be the Roman army in Germany is a sure sign things aren't going to work out.
It has become mythological to look at morals or american culture and say watch out, we'll be like Rome. But the structure of our government, our initiative, and freedom do not make us a good comparison. Nor is what really happened to Rome analogous to anything going on in the United States. Only useful to "the sky is falling" and uneducated types.