What would the problem be in just showing a button that says "Confirm unsubscribe" that sends a POST request? A lot of sites does something like that for their newsletter unsubscription.
I'm actually much more concerned when I don't have to click the link. It let's me know they haven't thought the problem through and what other errors and problems are there in their systems?
I believe asking to login violates the CAN-SPAM Act. That being said, there might be two links, one for "update commication preference" on top and "unsubscribe" in small text at the bottom. I always ignore the first and seek the latter.
