You don't have any way of defending against that stupid scenario, with or without centralized passwords. Additionally, most of the users would probably use the

You don't have any way of defending against that stupid scenario, with or without centralized passwords. Additionally, most of the users would probably use the same password for each of the services anyway, so you have pretty much the same situation in both cases, only you don't have a quick and reliable way to invalidate all the passwords.