Can't unsubscribe without logging in

Users can subscribe to a mailinglist without logging in on manage/lists/$list/. In this case, they receive a "please confirm your subscription" mail.

However, it's impossible to unsubscribe without logging in.

The most boring ;-) solution would be to extend the subscribe form with another button labeled "Unsubscribe". Here's a quick mockup:

Clicking the "unsubscribe" button should trigger a "please confirm your unsubscription" mail.