The problem with materialism is a very specific kind of materialism known as "eliminative materialism" which tries to eliminate consciousness and by implication the supernatural, which is essentially a form of consciousness believed to exist seperately of the brain. As a materialist and an atheist, this is an extremely crude and primitive position which is ultimately nihilistic as in rejecting consciousness it also causes serious problems for the concept of truth and ethics.
In dialectical materialism (the marxist variety) consciousness is a property of matter, and matter is primary. The idea that consciousness can exist independently of the brain is the basis for religious belief and is dismissed as an illusion. This is why materialism and religion belief are opposed as they assert different causes for pheneomena; idealism argues it is the mind, idea, spirit, god, etc, whereas materialism says it is independent of the mind. Marxism does not catagorically say that religion is false, but that by an error of abstract thinking we have misattributed the cause of pheneomena to god, etc.
If consciousness is a property of matter and a result of the activity of the brain, we can establish that it does exist without needing to rely on our own internal sensation of thought. So I do not accept the idea that we can only be aware of our own consciousness.