Each time this button is clicked by a recipient both the ISP and Email Marketing take note. This negatively impacts your delivery and our ability to ensure impeccable delivery for all our senders. This is why we take this so seriously.
If you get too many complaints, you run the risk of your service being interrupted, or your account suspended. "Too many", as defined by industry best practices, means more than 1 spam complaint for every 1,000 emails sent. We are sensitive to the fact that different types of emails get different types of responses, but this is a good rule of thumb to keep in mind.