It should only take one click on the unsubscribe link in the email for the sender to actually do the unsubscribe. If after processing it the sender is determined to try and stuff a sales and marketing survey on the landing page, I suppose it's hard to stop them, but I won't play "20 questions" just to get the sender to accept that I don't want any more of their emails.

Executive summary: if I can't unsubscribe from your email newsletter with one click, you get the spam filter treatment <sigh>