I think at LEAST half of them don't even know it. I have been amazed by the number of self-professed devout xians who know NOTHING about the history, foundation and dogma of their religon, let alone it's blood-soaked past.. Those who DO know about it want to excuse it as 'normal at the time' history, or attempt to validate it with replacement theology. But in fact, I think most of them don't know. Remember, you have to search for the truth. You have to pursue knowledge. They are taught that searching outside of their NT is caused by a lack of faith, and that faith has nothing to do with intelliegence, therefore further exploration of the history and truth of the church is "a sin".
Pretty good control mechanism the church established, isn't it?
But in my experience, most of them don't know, and when they are taught it, they don't want to talk about it, and when pushed to talk about it, they excuse it.