[svnt]

What do you mean we can’t build them?

To your second point, we have little to no ability to understand yet what quantum effects may or may not be active in brain/consciousness function. We certainly can’t exclude the possibility.

[Filligree]

I mean lots of people have tried to build quantum computers, and so far no-one has succeeded in anything that's describable as a "computer", instead of "half a dozen logic gates". Perhaps in the future.

We can fairly well exclude the possibility of interesting quantum effects in human consciousness, because the human brain is a hot, dense environment that might as well have been literally designed to eliminate the possibility. It's the exact opposite of how you want a quantum computer to be built.

Which doesn't mean there aren't plenty of quantum effects involved in the molecular physics, but that isn't what is normally meant by 'quantum computer'. Transistors would also meet that definition.

[svnt]

I do not agree with either of your assertions:

1) That 433 qubits does not make a computer and is instead “a half dozen logic gates.” I agree a half dozen logic gates is not a computer. 433 qubits is not comparable in terms of information capacity or processing capacity to a half dozen logic gates. This number is also publicly doubling annually now — I would bet the systems we don’t know about are more complex. Importantly, a computer in this context is not something you would attach a monitor to — it is just an electronic device for storing and processing data.

2) That we have any good idea of the limits of how biological systems might be influenced by quantum effects within specific temperature ranges. You certainly wouldn’t construct a human brain to interface with quantum effects given the present state of our knowledge in constructing these kinds of systems. But then we can’t even construct a self-replicating cell yet, nevermind a brain. It’s hard to imagine we understand the limits at work there.