This is what MailChimp does for its one-click unsubscribes.

You visit a URL, and some JS POSTs to `https://[youraccount].us1.list-manage.com/unsubscribe/post` with a body containing your subscription and list IDs.

I'm not sure what prevents crawlers executing JavaScript on that page and triggering the unsubscribe action anyway, though, unless it's just that email crawlers don't execute JS.