If they sent out a survey about "why you're no longer a customer" I suppose it would provide one channel for explaining one's actions. Oddly, I seem to get those constantly when I am a customer, but essentially never when I'm a former or inactive customer.
On privacy grounds I like the idea that non-customers would be left alone, but on boycott-impact grounds it seems like having some kind of predictable "what are we doing wrong?" channel would be nice too.