Email addresses are nearly useless if they're not public.

That I disagree with. Email addresses are nearly useless if noone knows them, but addresses known to a proper subset of the world population can be quite handy. I've various public email addresses. I've also tons of email addresses only a few number of people know. I even have email addresses only one person beside myself knows. Except for some of the public addresses (which only get spam), all of them are useful.

Email addresses aren't that different from phone numbers. Just because a number is unlisted doesn't mean it carries no use.