I hope you realise not all Christians are against the 18+ rating....
As a Christian myself, I wrote a submission to have an 18+ rating for video games. From what I understand, a lot of people supported this, but the government still hasn't acted (*frustrated sigh*).
I also spoke with my other Christian friends who are also gamers. To them, an 18+ rating for games is a logical choice. Unfortunately, they're all Americans and they have an 18+ rating over there already.
I agree that the ACL is not always in touch with the actual situation though!