No Warren, it's not lunacy. And saying so is most certainly uncivil. I don't know who constitutes "SDAs as a group." But I believe SDAs overwhelmingly endorse the doctrine of Sola Scriptura. The fact that you can find intellectual inconsistency in their professed belief doesn't mean they don't believe it. 

Just about everyone, including you and me, has beliefs that demonstrate little need for intellectual consistency. We just rationalize away the inconsistency. It's not lunacy. It's human nature to simultaneously hold positions that seem quite inconsistent to others who do not share those views. Fundamentalists - both liberal and conservative - tend to have difficulty seeing this characteristic in themselves and accepting it in others.