You have to prove it is/can be conscious, not the other way around.
The author is trying to positively assert that it’s impossible that AIs have consciousness.
I think you’d be hard pressed to find even the most ardent of AI proponents claiming AIs are _definitely_ conscious. They are almost always claiming something weaker, which is that it is possible.
We don’t have a precise enough definition to do either.
"They can't be intelligent as they lack consciousness"
"Ok then how does intelligence require consciousness? What is consciousness? How could one prove that someone or something has consciousness?"
"That's on you."
No, no it is not. If consciousness is a prerequisite for intelligence or moral patience, then it is on the proponents to define exactly what that is and how to prove it.
On matters of moral patience especially, we should err on the side of caution, because the cost of getting it wrong is catastrophic.
Imagine if we actually demanded that you prove your consciousness before we believe you.