Cat's are obviously conscious in the sense of the dictionary definition "aware of and responding to one's surroundings; awake." Unless you knock one out or similar.
Arguing they are not conscious in the sense of a more obscure definition is a bit pointless unless you specify your definition.
Theres a huge difference between reactive and conscious. Conscious cant even be verified for humans other than ones' self. Theres absolutely no reason to believe cats are not conscious.
There's also no reason to believe, e.g., rocks are not conscious, if your position is that we have no idea what consciousness is or where it comes from.
If you take the view that consciousness somehow arises from the brain and neural connections (which is intuitively plausible, but I personally am skeptical), it stands to reason that other species with complex brains are conscious as well. Perhaps "less conscious" (if that means anything) in proportion to how much less complex their brains are.
It doesn't make sense to have a scale of consciousness. The argument that consciousness is a manifestation of a complex brain is rather weak. Either an organism knows about self, and therefore tries to preserve self. Or it doesn't. I don't see how an in between exists.
Yes. They have been shown to be self-aware and aware of their surroundings, which satisfies the classical definition of consciousness. Unless you reject that definition, I'm not sure why you'd claim this.
Cats haven't expressed self-recognition in the MSR test. However humans younger than 18 months also don't pass that test. So to say it is a measure of conciousness is quite a stretch.
I'm not an expert either, but my understanding is that "consciousness" is still so poorly understood that it's more the realm of philosophy than science.
In particular, we all know that we're conscious, but can't really explain what that means.
How do you know?