Well, people have lot of different answers, some of them pretty ridiculous.
One fundamental reason why this is such a controversial and confusing topic with a wide range of opinions is that consciousness is meta-physical phenomenon. I.e. it's out of the scope of science in a way. But the concept that there's something beyond science is completely unintuitive to many people (by "beyond science" I obviously don't mean BS like spirituality etc., it's from a purely rational perspective). So trying to understand consciousness with science only will inevitably fail.
One fundamental reason why this is such a controversial and confusing topic with a wide range of opinions is that consciousness is meta-physical phenomenon. I.e. it's out of the scope of science in a way. But the concept that there's something beyond science is completely unintuitive to many people (by "beyond science" I obviously don't mean BS like spirituality etc., it's from a purely rational perspective). So trying to understand consciousness with science only will inevitably fail.