Do you then store the email address after having sent the link to the user? Because I don't think people view it as "giving their email address", but more like "send me the link and forget that you ever saw my email address".
Storing emails would be a convenient way to send the link if the user did not send it from the registration page or lost it in the meantime. As a user I would love seeing this kind of identification and would probably set a email account only used to recover links and avoid sharing my main email account.
