Freeform Pro Plugin Mailchimp integration
I had this same issue. We needed to send a contact information form to MailChimp only if the person opted in to receive e-mails. However, the information would always be sent even if the opt-in box was left unchecked. No idea why. I ended up hiding the opt-in box and then added a "yes or no" field that conveyed whether or not the user wanted to receive e-mails. Hope that help and makes sense!