This claim has some interesting consequences. If all we are is matter and the matter that makes us up is constantly changing, it follows that there is nothing about us that stays the same over time. In the final analysis human beings are reducible to little more than a constantly shifting and changing bundle of perceptions. Here's Rosenberg:
Nevertheless, if the mind is the brain (and scientism can’t allow that it is anything else), we have to stop taking consciousness seriously as a source of knowledge or understanding about the mind, or the behavior the brain produces. And we have to stop taking our selves seriously too. We have to realize that there is no self, soul or enduring agent, no subject of the first-person pronoun, tracking its interior life while it also tracks much of what is going on around us. This self cannot be the whole body, or its brain, and there is no part of either that qualifies for being the self by way of numerical-identity over time.
There seems to be only one way we make sense of the person whose identity endures over time and over bodily change. This way is by positing a concrete but non-spatial entity with a point of view somewhere behind the eyes and between the ears in the middle of our heads. Since physics has excluded the existence of anything concrete but non-spatial, and since physics fixes all the facts, we have to give up this last illusion consciousness foists on us.What are the consequences of denying that there is an enduring self? One is surely the bizarre conclusion that we cannot be said to be the same person today that we were ten years ago. If we are in constant flux then we are different from the individual who went by our name in the past. Now, if this is true it would be unjust to be held responsible for anything that other person did. In the same way that it would be unjust to expect you to keep the promises made by another person, it would be unjust to expect me to keep promises made years ago by a person who had my same name. Marriage vows, for one example, would become worthless once people realized that it wasn't they who made them.
Furthermore, it would be unjust to punish criminals for a crime committed years ago because the person we're punishing is not the same person who committed the crime. For those of you familiar with the movie, we might ask this question: Is Jason Bourne responsible for that couple he killed in the Bourne Identity if he has no memory of killing them? Was it really he who killed them? Rosenberg would be hard pressed to explain how it would have been.
T.S. Eliot puts it like this: "What we know of other people is only our memory of the moments during which we knew them. And they have changed since then....at every meeting we are meeting a stranger."
This seems absurd, to be sure, but it is another of the consequences of naturalism that Rosenberg wants his fellow atheists to recognize and acknowledge. Little wonder that so many atheists are unwilling to stay with him on the atheism train all the way to it's logical endpoint. They can see that the tracks terminate at a precipice and that the train is going to hurtle over a cliff into the abyss of nihilism and so, still clutching their atheism, they jump off before it gets there.
This is, of course, irrational, but perhaps the most irrational thing they do after having jumped off the train, after having made a completely arbitrary, unwarranted, and irrational leap in order to avoid going over the cliff of their logic, they turn and point to the Christian (or other theist), whose worldview entails none of these problems, and tell them that it is they who have abandoned reason because they chose not to take the train at all.
One can only smile and shake one's head.