But it's not a good reason for adding unsubscribe links unilaterally to all email communications.
Remember, unsub links are machine-automatable; Gmail at least offers to follow any embedded unsubscribe links for you if you mark a message as spam. (Which, with hotkeys enabled, is one accidental keypress away.)
So consider the extreme case: what if the user fat-fingers an unsubscribe (without realizing) to their local electric company's e-invoices, which is what they've been relying on to prod them to log onto the site and pay the bill?
If it's clear that "bills you need to react to or your power will be shut off" shouldn't have an unsubscribe link, then clearly there's some sort of line that must be drawn somewhere.
(Note, I'm not arguing against the use of "Manage your Mail Preferences" links in these cases — the kind that act as magic sign-in links and take you directly to a page on which you can un-check a "mail me about X" checkbox. It makes sense to include those. I'm just arguing specifically against unilaterally including "Unsubscribe" links — the kind where following the link unsubscribes you with no further confirmation needed.)