I know the efforts put into Dateline (USA) and Fifth Estate (Canada) exposing the WTBS pedophile scandal caused many to stop and think. Some eventually even left.
I have heard with personalized letters of people when leaving sent to very close friends and family have had an impact. I haven't heard of any mass impersonalized mailing having success. It doesn't mean it can't or hasn't happened, just simply i haven't heard of it. fjtoth tried it when he left Bethel. He put a note under every single door of the Bethel residence. Between thsoe collected and destroyed and those simply thrown out, it didn't change anyone.
I was already doubting at the time and I didn't read past the first paragraph.
People should do what they feel they should do but don't browbeat others if they don't buy into personal campaigns.