There must be an algorithm that we can apply to show what such a change will have for society. If the probability is that the change is negligible, we should consider allowing it. But if the probability is that the change is overwhelmingly "bad", we should not allow it. Let's not argue from ignorance. What are the numbers? What are the ethics? For example: Say if we listened in on all connections, we would catch an e…
But is that in any way comparable with automated surveillance? I think a fitting analogue would be having every mail scanned and archived. Different circumstances...
I doubt the numbers game you are proposing would net any insights, since it has a hidden premise that child trafficking can only be prevented with restricting encryption.