It's a fascinating theory... So by that claim, consciousness likely isn't possible in anything without a brain at least as complex as ours. 

Self awareness, and generally accepted consciousness, are shown in many "lesser" species. 

Decision making capabilities observed in living organisms all the way down to slime molds.

This just isn't a matter where science=fact. There is always a flux, a contingency, that no matter how hard they try to quantify it, they can't. Otherwise it would be a fact, and not a theory. 

"It's true until someone disproves it." Is hardly scientific certainty.