Nay-sayers to instant-unsubscribe links in emails tend to defend bad practices by email clients that will read the link before the user activates it. Email clients do that in an attempt to precache the linked page, to make it show up faster when the user does activate the link. Of course by that time the unsubscribe action already happened.
The correct course of action is to use a better email client, that won’t act that badly.