"We are one" can also be said of a humanist. It is the recognition that we are all humans and the acknowledgement that my suffering is very well someone elses, and I should not do unto others what I do not like done unto me.
There isn't anything that you've argued for which is neither exclusive nor contingent on a world view which proposes all of this is a simulation. In other words you bring nothing to the table other than an assertion. No "oughts" to live by, no ultimate code of ethics, nothing.
If you truly treat others as if "we are all one" and you are steadily evolving towards love, then you are correct. Having a larger and more accurate picture of reality adds nothing behavior-wise. The only thing that can be offered beyond that is better understanding of the nature of existence.
In fact, it can be argued that such a world view can be toxic. Think Inception. If I genuinely believe this is all a simulation and I simply want to unplug, I can just off myself. Which is fine, but what if I also decide to end others because according to my own perception of this particular world view, I'd be doing them a favor.
In my view committing suicide is a waste of time. We are here to evolve and committing suicide only throws a wrench into the process and slows it down. I believe in reincarnation, either back into this reality or another like it. In this view killing others or yourself is not doing anyone any favors it's just causing a bunch of heart ache and unnecessary wasting of time and resources.
On the other hand if one believes that existence ceases at death then such a world view could be toxic. Consider someone who is convinced that existence is nothing but pain and suffering and therefore killing everyone and him/herself would be doing everyone a favor by ending all of the suffering. There is a thread on this forum started by such a person who does not wish to exist, and the belief that existence stops after physical death is toxic in this situation because he truly believes he has an "out". And so suicide is a logical conclusion according to your world view. So don't try to convince me that a belief that consciousness ceases at physical death is preferred behaviorally.
Also, someone who believes they are their brain and their physical body believes themselves to be a separate material object and therefore considers morality only a virtue but not an integrated part of the nature of reality. Selfishness and fear are the products of the belief that one is separated from the rest.
Further, "humanism" only has to do with "humans" whereas the concept that "We Are All One" includes all living creatures and whole of reality.
“A human being is a part of the whole called by us universe, a part limited in time and space. He experiences himself, his thoughts and feeling as something separated from the rest, a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty.” - Albert Einstein