Is there any particular reason to believe that a salads might be capable of consciousness? No
How can you tell without "any satisfactory theory of consciousness"?
The same way I don't need to understand aerodynamics to know that I have no reason to believe that turtles might be capable of flight. I've never seen a turtle do anything that sits in the neighbourhood of the notion of "flight" in the network of concepts in my head. This type of argument doesn't work against the putative consciousness of foetal brains, since we have good reason to believe that at least brains at a certain stage of development are in fact conscious. To argue that this means we can only have an ethical problem with running dubious...
This seems significant:
http://www.theguardian.com/science/2015/aug/18/first-almost-fully-formed-human-brain-grown-in-lab-researchers-claim