Have you ever gotten a bad reaction from these emails? Presumably the user had just expressed that they don't want anymore emails and they're getting another one :)
Not really. Some people don't respond, others just respond to the email with the reason and the remaning take us up on the offer and give us great feedback.
When unsubscribing from an email service most people would expect to get an email saying that you have successfully unsubscribed.
I actually tend to mark that SPAM if I get an email after I've unsubscribed.