We hold consciousness to be a marker of "something worthy of ethics" but it's a bit of a species solipsism. Consciousness is a biological process or effect. Why is it more important than other biological processes or effects? Well, because we're humans with "consciousness" and we think so.

To me, consciousness is likely to be explained as an emergent phenomenon allowing humans to collaborate, rather than something that is more akin to the "soul" or "self" that is often ascribed. To my mind, ethics, if we can separate that concept from other emergent phenomena, should be applied more holistically than just to things we believe are conscious.