  On the most natural interpretation, Sidgwick is noting various non-normative facts.  I have a distinct history, memories, and perhaps special access to my mental contents.  But it is not clear how these facts support the normative conclusion Sidgwick draws.  Utilitarians, for example, agree about these facts.  (Some of the facts may also not give the sharp distinction Sidgwick wants.  I may usually know more about my pain than yours, but this difference seems a matter of degree.)