I carefully look for “subscribe to news” checkboxes and always untick them; if you send me campaign emails without me explicitly opting in you are getting a spam flag, whether or not I gave you an address for transactional mail.
I try to use unsubscribe links when 1) they exist and 2) the email is from a legit organization that I reasonably believe is actually going to unsubscribe me from something (if not from every place they've copied my address to by now), but I can see the argument for just flagging as spam in the case where an organization oversteps previously agreed bounds. Especially with the political campaign emails, the unsubscribe game can feel like futile whack-a-mole.
For ordinary commercial campaigns, I'd worry that flagging as spam would cause legit transactional mail (i.e. mail that belongs in the Updates auto-label) from the same organization to get flagged as well, but based on the state of my Spam folder, that's already happening anyway...
If an unsolicited email contains no unsubscribe, that is bad behavior and they get spam tagged immediately.