John R. Searle is a non-theist who believes in biological naturalism. Wikipedia describes Searle's position as:

Searle denies Cartesian dualism, the idea that the mind is a separate kind of substance to the body, as this contradicts our entire understanding of physics, and unlike Descartes, he does not bring God into the problem. Indeed, Searle denies any kind of dualism, the traditional alternative to monism, claiming the distinction is a mistake. He rejects the idea that because the mind is not objectively viewable, it does not fall under the rubric of physics.

If one has consciousness coming from a program running on a Turing machine, which is what I assume is meant by "artificial consciousness", one has dualism. He expressed this concern in his paper describing the Chinese Room Argument:

This form of dualism is not the traditional Cartesian variety that claims there are two sorts of substances, but it is Cartesian in the sense that it insists that what is specifically mental about the mind has no intrinsic connection with the actual properties of the brain. This underlying dualism is masked from us by the fact that AI literature contains frequent fulminations against "dualism'-; what the authors seem to be unaware of is that their position presupposes a strong version of dualism.

So, one reason for non-theists to reject artificial consciousness is because it implies a strong form of dualism. When one moves the program from machine to machine, if that program is indeed our minds, then we have gone through an out-of-body process to be reincarnated in another body.

Searle, J. R. (1980). Minds, brains, and programs. Behavioral and brain sciences, 3(3), 417-424.

Wikipedia contributors. (2019, February 5). Biological naturalism. In Wikipedia, The Free Encyclopedia. Retrieved 19:20, April 22, 2019, from https://en.wikipedia.org/w/index.php?title=Biological_naturalism&oldid=881932833

John R. Searle is a non-theist who believes in biological naturalism. Wikipedia describes Searle's position as:

Searle denies Cartesian dualism, the idea that the mind is a separate kind of substance to the body, as this contradicts our entire understanding of physics, and unlike Descartes, he does not bring God into the problem. Indeed, Searle denies any kind of dualism, the traditional alternative to monism, claiming the distinction is a mistake. He rejects the idea that because the mind is not objectively viewable, it does not fall under the rubric of physics.

If one has consciousness coming from a program running on a Turing machine, which is what I assume is meant by "artificial consciousness", one has dualism.

Searle expressed his concern against the dualism of strong AI in his paper, Minds, Brains and Programs, where he described the Chinese Room Argument:

This form of dualism is not the traditional Cartesian variety that claims there are two sorts of substances, but it is Cartesian in the sense that it insists that what is specifically mental about the mind has no intrinsic connection with the actual properties of the brain. This underlying dualism is masked from us by the fact that AI literature contains frequent fulminations against "dualism'-; what the authors seem to be unaware of is that their position presupposes a strong version of dualism.

So, one reason for non-theists to reject artificial consciousness is because it implies a strong form of dualism. When one moves the program from machine to machine, if that program is indeed our minds, then we have gone through an out-of-body process to be reincarnated in another body.

Searle, J. R. (1980). Minds, brains, and programs. Behavioral and brain sciences, 3(3), 417-424.

Wikipedia contributors. (2019, February 5). Biological naturalism. In Wikipedia, The Free Encyclopedia. Retrieved 19:20, April 22, 2019, from https://en.wikipedia.org/w/index.php?title=Biological_naturalism&oldid=881932833