Well, Ian, established religious tenets also get stringently questioned and debated periodically in most major religions, and doctrine gets changed after much furious discussion between the learned minds at the top of the authority structure. Such debates and schisms have frequently rocked even an ossified structure like the Vatican over the past centuries and they led, among other things, to the Protestant Reformation.

There have been several such schisms in the Muslim faith too. And in the Jewish faith. And the Buddhist faith. Etc.

It doesn't just happen that way in the world of science. Religion, like science, can be a field of continual inquiry, not just a field of rigid, established belief.

The conservatives in religions are the ones who cling to the old beliefs and defend them. The liberals and radicals challenge the old beliefs and change them. The same is generally true in science (where new theories and new interpretations of existing evidence are frequently brought forward to challenge the old ones...and are often bitterly resisted, even ridiculed, by the conservatives in the scientific establishment).