That's a bad example, "programmatically unsubscribing" means giving spammers information that this address is alive. A much better solution is to report the unwanted email as SPAM, so the sender's reputation takes a hit.

(and for that 1% of the cases where the address is not a spammer and user knows it, they can just hit "unsubscribe" manually)

I’m talking about subscription services a user signed up for at one time

That's a bad example, there's already the List-Unsubscribe header.

Subscription services like Netflix, not emails.