But that works the other way around too. Somewhere hidden in the brain of a a liberal western person is a murderer/terrorist/child abuser/fundamentalist if you just perform the right set of edits.

Again, not all beliefs are equal. You don't want to use the procedure that'll find a murderer in yourself, you want to use the procedure that'll find a nice fellow in a murderer. And given such a procedure, you won't need to exclude murderers from extrapolated volition.