Why does everyone assume that they are conscious?

I'm not saying that they aren't but thinking that they are is just dumb. We don't even fully understand consciousness yet so saying that throwing a bunch of thoughts and sensory inputs together in a biological brain is consciousness is dumb.

Intelligence we know can be tested but the only evidence we have of consciousness is subjective and even then it's purely anecdotal. To suggest that it would just pop up in every human brain that exists is dumb.

Of course consciousness could be normal in humans, but there's no bulletproof evidence that they are. I don't think many people are conscious because then they would realise that they are slaves not free beings.