The statement that there is no afterlife is equivalent to the statement that the sun is not made of spaghetti. There's no possible math, context, perspective, or arrangement of facts that would allow the sun to be made of spaghetti.
Your consciousness resides in your neocortex, the thin sheet of neurons on the surface of your brain. We know this because when injury or illness disrupts or damages its operation, your consciousness goes away. It's maintained if there's injury or illness anywhere else.
There's no room for disembodied mystery. There's no room in the laws of physics for information transfer such that the pattern of physical connections and electrochemical activity in your brain to be communicated intact when you die. Everything we know about the universe leaves no mechanism for your mind to continue after biological death.
We will eventually scan brains, and at some point we might be able to extend our minds into machines and maintain our consciousness after the biological parts die. We don't know enough about the nuanced particulars of neuroscience but the challenges are a matter of resolution, scale, signal strength, and not damaging a living system. There's no mystery to the phenomena of consciousness allowed by laws of physics.
Multiverse or simulation theory leaves room for some different level of reality where the substrate of your mind resides. Those are interesting abstractions, but there's no evidence or theory to suggest either of those contexts are valid.
It's not arrogant to assert that the moon isn't made of cheese or the sun is not made of pasta, or that there is no life after death.
It seems to me that insisting on those things in the face of evidence would be arrogant, as you would be claiming that you know better than everything that can be proven, all of those things for which we have evidence and explanation.