Giving up 3 would imply that our values are rather arbitrary

Is that even in question? If these values (whatever they are in a given person) can be derived from some higher value, then they may not be arbitrary, but at some point you're either going to find a supergoal that all values derive from, or you're going to find two values that are arbitrary with respect to each other.

Finding the latter case sooner rather than later seems to match how humans really are, so unless you're willing to argue that humans have a supergoal, giving up 3 is a step that you've already taken anyway.