Confirmed subscribers reporting spam

Hi

How do I try and deter confirmed, engaged, double-opted-in subscribers from reporting spam? We do not send a high volume of newsletters, and we have a very tightly managed, very clean list of only double-opted-in confirmed subscribers. Subscribers are very engaged and yet, nearly every campaign someone reports a spam, even though - when I look them up - I see that they have opened all our emails since subscribing. Really annoying - how can people be educated that spam complaint rates damage our reputation?! Why do they not realise that just because they don’t want to subscribe any more is not a spam reason?!

Thanks