> 1. Anything that already exists, the universe is able to construct

I didn't claim it is possible we couldn't build meat brains. I claimed it is possible that equivalent or better performance might only be obtainable by meats brains.

> 2. There is no "magic". Anything that happens ultimately follows the rules of nature, which are observable, and open to understanding and manipulation by humans.

I actually don't believe the last part. There are quite plausibly laws of nature that we can't understand. I think it's actually pretty presumptuous that we will/can eventually understand and master every law of nature.

We've already proven that we can't prove every true thing about natural numbers. I think there might well be limits on what is knowable about our universe (atleast from inside of it.)

> 4. Ergo, while it might be difficult, there is fundamentally no reason to believe that the creation of an intelligent object is outside the capabilities of humans.

I didn't say that I believed that humans can't create intelligent objects. I believe we probably can and depending on how you want to define "intelligence", we already have.

What I said is that it is not a forgone conclusion that we will create "a better therapist, doctor, architect". I think it is pretty likely but not certain.