Materialists find it reasonable to suppose consciousness is an illusion. Were consciousness illusory, what are the rational conclusions? How would materialists act differently than they did before? They shouldn’t – logically, there’s probably no consequences. However, if materialists manage to get it widely accepted, they’ll use it for coercion. They’ll say your dislike for policy X is illusory, and therefore not a reason to oppose it.
Consciousness is the fundamental quality of humanity. For example, if language or planning make us not like other animals, then we have those things because we first evolved full-blown consciousness. If humanity has a purpose, it involves consciousness somehow, both because of the above, and because passions precede reasons. Values require consciousness, and it is in service of values that reason is employed.
Primarily what humans care about, what humans value, are other consciousnesses. If there is a god instinct, then humans wish to find a superior consciousness and put themselves in service to it. If the god instinct is just another cultural mind-virus, then humans wish to serve their own consciousness, and those of their friends and family. This latter may be a contingent result of having evolved to be a social species, but also it may be a necessary result of having evolved consciousness. Materialism, like any philosophy, should serve its hosts. Having the hosts serve materialism is sublimely perverse. Of necessity, materialism denies that the host can be subjectively served.
Note that many powerful materialists use the philosophy cynically, for their own benefit, without truly believing. I happen to doubt the Pope is Christian either.
Consciousness is the tool through which you appreciate everything else. A thing with no conscious manifestation is a thing that doesn’t exist. For example, we can’t feel nuclear radiation directly. But, we can hear clicks on a Geiger counter, and we certainly feel it if we die of cancer. If consciousness is an illusion, existence is an illusion.