You'll speak with a Christian and he'll say that even a very early fetus is conscious. Speak with other people, and it isn't. Some vegans say animals are conscious. Others don't. It's possible there's something real behind all of those people's definition of consciousness, and the real problem isn't that some are right and some are wrong.
They just disagree because it means different things for them, they just happen to be using the same word. The meaning of "consciousness" is more of a reflection of the values of the speaker than something real.