Paul Haggis, an Oscar-winning movie writer, has publicly left the Church of Scientology and made his resignation letter public, which can be read here.
I highlight this letter because of its focus and rationality. Haggis can admit to the positive aspects Scientology brought to his life while still denouncing the organization. Moreover, his denouncement is specific. He cites two specific issues rather than hurling random insults.
Also, both issues are fairly verifiable. Often, complaints against the Church of Scientology involve matters completely within the Church, and the evidence is hearsay. That doesn't mean the issues don't exist, but it does mean the public has little to work with beyond a storm of opinions and he-said/she-said battles.