Yeah I find it really annoying also. But surprisingly, they don’t do that just to add friction to unsubscribe. There is a real problem that it solves.
Legitimate mailing lists have problems with people forwarding emails, when the recipients of the forwarded emails click the unsubscribe button, they will unsubscribe the original recipient who didn’t want to be unsubscribed.
So why do they forward those emails to someone in the first place? Especially to those who don’t want them? You’re pretty much suggesting that “helping others spamming people isn’t spamming”
Whether or not an individual forwarding an email to another individual is technically "spamming" is moot; most spam is company-to-individual/automated-system-to-individual.
As to why they forward it in the first place: how would I, an individual, know whether or not my mom will want to use the 20% coupon code for a cosmetics store I just received, but don't want to use? I'd ask her. I can ask her via an unsolicited phone call or email. Am I a spammer if I do that?
Similarly, if my mom clicks the "unsubscribe" link on what I forwarded, mistakenly thinking that it was sent to her directly by $costmetics_company, that sucks for me if I ever want to use their coupons.
An even more annoying situation is when someone in charge of procurement for a business forwards a "shipping confirmation" email to an employee as a means of indicating that the employee's requested purchase is on its way. If that employee makes a mistake (e.g. they have a lot of commercial email in their inbox and click the wrong one/are sleepy/whatever) and clicks "unsubscribe" on that shipping confirmation, the procurement person won't get any future confirmations for any orders for anyone.
There are mitigations to this (the shipper could use transactional emails without unsubscribe links, the procurement person could do something less lazy than just forwarding the email wholesale), but in the real world those often don't happen. So autofilled unsubscribe then causes problems for random upstream people, not the forwarded recipient.
That is a problem with the implementation that is simply fixable by removing the unsubscribe headers from the forwarded emails. Or marking unsubscribe links in a way that makes the forwarder remove them automatically.
Someone on the other hand was trying to wave away the whole idea of one-click unsubscribe due to this which seems to me more like lobbying towards adding another step requiring one to put their email in in order to unsubscribe (or put it another way - decreasing the unsubscribes).
So auto filled unsubscribe needs to exist. I never want to go back to the universe where that is not regulated and easy-to-use. Also in the UK there’s still loads of physical paper spam and I would hate if that was also the case for e-mails.
Legitimate mailing lists have problems with people forwarding emails, when the recipients of the forwarded emails click the unsubscribe button, they will unsubscribe the original recipient who didn’t want to be unsubscribed.