Would it be possible to add a confirmation screen after you click on it? Like: WARNING! Clicking "Confirm" will empty the list of all its existing members, regardless of what was entered on the previous screen. That operation cannot be reversed. Are you absolutely sure that you want no one to be on your list anymore?
The reason is that we've had a lot of list owners who populate the "Emails to Unsubscribe" box on the "Mass Removal" page with a subset of the list's subscribers and proceed to click "Unsubscribe all" with the expectation that "all" means all the users explicitly listed in the box. Which means that the site admins have to restore the entire list of subscribers every time...
If adding a confirmation screen isn't straightforward, maybe the wording on the buttons could be modified:
Unsubscribe users -> Unsubscribe users listed above
Unsubscribe all -> Empty list of all its existing members (irreversible)!!!
In the meantime, this was problematic enough for us that my colleague Dan had to resort to hiding the "Unsubscribe all" button from the web page(s), which isn't ideal.