I ignore them mainly because it's easier. Facebook alone might send me 10 emails a day begging me to come back.
If someone was smart, clicking the unsubscribe link would only validate that the address the mailer was sent to was being used. I suspect that several services do this either via the unsubscribe link or a pixel tracker.
Most of the unwanted mail I see (at least what makes it past the basic automated filters) is from legitimate companies who think I'd like to hear about product updates every two days rather than Viagra pills or whatever.
If someone was smart, clicking the unsubscribe link would only validate that the address the mailer was sent to was being used. I suspect that several services do this either via the unsubscribe link or a pixel tracker.