I'm not sure I agree with you that Christianity is a failure as an ally in liberty.

Christianity has been a driving force for liberty in the west. The magna carta was drafted by the archbishop of Canterbury and is considered one of the founding documents of modern liberty.

Concepts such as all men being created equal and the idea of one law that applies to everyone are direct descendants of Christianity.

It was under such circumstances that the freest societies in the history of the world developed. They didn't develop in China which was technologically superior for much of its history, nor any other part of the world. It developed in the west due to a confluence of factors including the influence of Christianity.

It hasn't always been perfect and has its own scores of black marks, but if there's one thing I've been gaining an appreciation for it's the unusual society we're living in that's based on a really strange ideology that has led us to have the attitudes we have. If we didn't have certain factors people want to get rid of, it's likely we never would have developed to even care about something like liberty in the first place.