Disagreeing positions don't add up just because they share a feature. On the contrary, If people offer lots of different contradictory reasons for a conclusion (even if each individual has consistent beliefs) it is a sign that they are rationalizing their position.

If 2/3's of experts support proposition G , 1/3 because of reason A while rejecting B, and 1/3 because of reason B while rejecting A, and the remaining 1/3 reject A and B; then the majority Reject A, and the majority Reject B. G should not be treated as a reasonable majority view.

This should be clear if A is the koran and B is the bible.

If we're going to add up expert views, we need to add up what experts consider important about a question, not features of their conclusions.

You shouldn't add up two experts if they would consider each other's arguments irrational. That's ignoring their expertise.