It sounds more like they're providing an email to every user with the options set to public by default. While that could be construed as bad, it shouldn't override another email if that other email is marked as public.
It didn't replace, in my experience. I didn't know this was to be A Thing, and last week I was going through my settings and noticed the facebook.com address. "Huh, I guess they're adding email addresses to the existing URLs everybody has (or was able to sign up for those years ago)." My other (login) email address was still there, but as an alternate or whatever.
Look closer. Your previously public non-facebook address is now set as hidden. People attempting to email you will be forced through Facebook. "Hide from Timeline" option will be chosen.
The drama comes in Facebook automatically hiding your original email address, regardless of your original settings. There's nothing about that action that can be construed as anything other than forcing you into Facebook's messaging system.
