Good companies will require verification before sending anything else. Those I can ignore and they’ll go away. For the others, I make a good faith effort to unsubscribe, but a small one. They get about ten seconds for me to find the unsubscribe link, otherwise they get reported as spam. I’ve had some which won’t let me unsubscribe unless I log in to the corresponding account, which of course I can’t do.
Just remember that this stuff is spam. You’re not abusing a tool to your advantage, you’re using it the way it’s supposed to be used. Spam doesn’t have to be knockoff viagra or whatever.