I guess I always assumed that spammers didn't particularly care whether what they do is legal or not (and certainly that they didn't much care whether the people they contacted wanted to get their messages). Is this a flawed impression/prejudice left over from the ancient days of the internet? Because I've been floored by the number of folks here on HN saying that they click the "unsubscribe" link within an email for any reason, let alone in preference to their email provider's internal "spam" button.

Well, let's be clear: I wouldn't advise clicking anything in a V1@GRA-type likely illegal spam message.

But if we're talking about newsletters your don't remember signing up for or marketing emails or invites to a new social network, the unsubscribe usually works and will almost never harm you. AFAIK it's a myth that there's this huge black market for "valid" email addresses. Spammers don't want a list of people who click unsubscribe; they ain't gonna buy anything. There are way easier ways to find email addresses on the internet. And it would be crazy (and possibly illegal) for any sort of semi-legit company to sell their unsubscribe list.

Anything send by an actual company -- especially anything sent through any of the major email providers -- will almost certainly have a working unsubscribe. It's almost impossible to send a message in MailChimp without a working unsubscribe.