on My site, I wanted to hide user's email addresses, but allow the administrators to be emailed from the profile page.
I didn't want to alter or modify the profile page. I wanted to set, by default, end user's email not to be shown.
I used V@no's suggestion above and reversed it.
I added the following code to register_form.html
<input type="hidden" name="user_showemail" value="1">
Now my administrator's can be emailed from their profile, but all new registered user's email's are not visible in their profile unless they turn it on.