The one exception I can think of off the top of my head is MTV Networks, who got a hold of my email somehow and won't stop spamming me, even after I've unsubscribed at least a dozen times.
Why should I have to do extra work just because MTV is hostile to users? Or because Hallmark's database takes 10 days to update, gamespot's unsubscribe servers are permanently broken, or because some crappy website demands your login info?
http://imgur.com/mzqKk http://imgur.com/Yn5eD http://i.imgur.com/yoky5.jpg
And usually they don't really take 10 days, but that's the limit the law permits so they give themselves as much wiggle room as possible.
1. It's not "harsh" to mark anything as spam in your email; the only person it affects is you. The sender will not, of course, even know whether you've classified their stuff as spam.
2. Some commenters are claiming that it's not that much extra effort to visit the sender's site and unsubscribe yourself. This is manifestly not always the case, and more to the point, the user does not KNOW in advance whether it will be the case, when starting the process. However, hitting a plonk button in your mail client will always have a known time-suck-factor in advance.
3. Hitting a plonk button is also, of course, guaranteed to be at least one page-load and one click easier than any possible solution involving visiting a sender's website. Even if there's an unsub link in the spammy email itself, a plonk button is still one page-load less, and easier to find from a UI standpoint. So in sum, plonk is guaranteed to win from on ease of use. Not even a debatable question.
4. Some argue that taking time to unsubscribe yourself via the sender's website is just "the right thing to do", given that you subscribed to their emails in the first place. It seems to me that it should be incumbent on the marketer, not the customer, to make unsubscribing as easy as possible, and to "do the right thing". This should be the default.
To put it simple: the spam button is for spam = unwanted mass mails, mostly ads. For unwanted mail from specific users, you should create a filter.
My personal take on this though is: People who found out how to subscribe to a mailing list, should also be able to unsubscribe.
Spam is unsolicited. If you've signed up for a newsletter, or similar, then you've requested the messages.