Earlier quoted context omitted.
It is good practise. You should never use the unsubscribe function as it tells sender the account receives is actually in use and valid. Thus they will sell your email to even more spammers.
Yeah no. Emails which include an unsubscribe link are legit enough to not do that. Actual spammers don't bother to include an unsubscribe link.
If you want to get people to click a link in your malicious booby trapped email, then an "unsubscribe" one is high on the list to include. :)