People mostly define belief as something religous, a thing an atheist didn't have because he or she is rational, but in my opinion every human being has a belief of how the world is shaped and how it's inner structures works.
It is not your belief which defines wether youre a sane person or not, it is how much the universe agrees with your belief. It is totally legitimate to belief in fairy-unicorns and purple dragons but just by your belief they wont come into existence when there is no place in the universe for them to exist. You can say that the universe, not a human instance, has to agree wether or not your belief has any referencepoint to it and works according within the laws of its inner structures. Aristotle believed that things fall down because it is the proper place for them to be, which is totally accurate. And Sir Isaac Newton could put the laws of gravity into formulas but he wasnt any further as Aristotle to explain why things fall down. This comes first with Albert Einstein. So even an rational, scientific mind has a belief in how the universe functions. Only the Atheist is an Atheoi. One who does not belief in the existence of personal gods as entities.
Every human subject has beliefs about the universe, a subjective perspective, no matter how crude or rational. If we share our beliefs with others, gain consent we have a shared belief, an intersubjective perspective of the universe, not as individual, but as group. At the point you organize the shared belief, put authority over others on it and hierarchy you can speak about religion, which is in my opinion not an end in it self but has a purpose.
For emperor Constantine christianity was given the purpose to represent the inner glue which should prevent the roman empire from falling apart, a heritage reaching still into the present time. For Marx, christianity was an opium for the masses, which nauseate the people with messages which lures them into the truth that there is no change possible, the structure of society is without alternative because its handed down by god. For the chinese emperors the confucian ethics were the fundament and concrete to build a stable society from the early ages.
Religion as hierarchical authoritarian organized system is a structure of power as Constantine and Marx were well aware. Whom controlls the fabric of truth controls the people woven in this fabric. If you are cultivated within the so called western civilisation try for better reflection the image of fanatic djihadists which are alone in posession of the one and only truth. Same goes for a lot of people. Catholics, Trump sympathisants, orthodox christians, Jehovas witnesses but also people whom are not critical about the temporary social discourse. They are woven in their individual cultural narrative structure. And this is also true for atheists. Being an atheist just means that one does not belief in supernatural beings controlling the doings of the universe or even made it. It means not that an individual is not part of a intersubjektive pattern of truth.
Foucault states that in every society or social sphere were and are agents which are producents of truth. This means that were are individuals or groups of individuals which are able to partizipate and create on the narrative of intersubjective truth, or better said, which have write permission on the reality of their groups. This could be politicians, leaders, diplomates, priests, shamen and not to underestimate artisians, singer, poets. Today in our modern times we have also professional newsagents, reporter and scientists which are shaping the fabric of our truth.
Religion is shared belief mixed with political structures. In Religion is a power-structure for masses. That is in essence the critique of Marx about religion. What in my experience the great mistake of great parts of the political left is that they expand the term religion on every stream of belief which is their intersubjective reality non-rational or theist, ignorant to the fact that they are too part of a shared narrative of truth which is today called ideology. It seems to me that religion and ideology has a lot of in common. Holy rituals, holy prayers, high temples and holy symbols and values. Believing in supernatural beings is not consequently part of it. If you have any doubts about my hypothesis just compare with the soviet ideology in times of the soviet union or the national narrative of the USA. The place is full with rituals, prayers and symbols.
This is not a sermon against spirituality and belief but it is about a critique of organized religion. In my opinion it is more interesting to establish an intersubjective reality as a distributed open-source system. You may say, we have the scientific peer-review process, which I would agree is the best established system we have. Problem is in my opinion that underneath this process, and this is knownfact, are underlying powerstructure of privilege, of established persons and groups, of the bourgeois intellectual who defend the actual paradigma because he profits from it.
"If an idea does not appear bizarre, there is no hope for it."
Nils Bohr