The basic issue in philosophy is the struggle between materialism and idealism. In philosophy, materialism means that material reality - the stars and planets, the atoms and molecules, heat and light - existed before thought. Idealism is the opposite.
Idealists believe that thought—in the form of God, order,  spirit, destiny, fate, karma, or human consciousness—came first. Materialists believe that thought reflects matter. Idealists believe that matter reflects thought. Communists are materialists.
As pushers of idealism, the capitalists are similar to earlier ruling classes. The enslavers of ancient times and the feudal lords of the Middle Ages used religious ideas to keep the enslaved and serfs from rebelling. For example, they said the pharaoh, emperor, or king was God, or at least a direct representative of God on earth, and therefore had to be obeyed. Lesser ruling-class figures were indirect representatives of this divine power.
Serfs were told that life on earth might be hell, but disobedience to these God-chosen rulers was a sin that would lead not only to immediate punishment, but to eternal hell. Passive obedience, on the other hand, would be rewarded after death by an eternal afterlife in heaven.
Idealism can't stop rebellion
Religious forms of idealism still influence many people, because they offer security and care, even if imaginary, to those who suffer from the real insecurity and harshness of capitalism. And they offer rationalizations to those who fear fighting back.
However, in an age before the development of science, when superstition was virtually universal because it appeared to be the only way to explain nature, religious idealism was an even more powerful weapon against the masses. Despite this indoctrination, people fought back, at times even inventing other “Gods” to justify their actions.
During antiquity and the Middle Ages there were thousands of rebellions by slaves and serfs, such as the revolt led by Spartacus in ancient Rome, and the Peasant Wars in Germany during the 16th Century. These revolts were put down by the organized violence of the state, often only after prolonged armed struggle, and often followed by mass executions of the rebels and anyone suspected of supporting them.
The crime? Astronomy. The penalty? Death
Even people not directly involved in class struggle were attacked. The Italian philosopher Giordano Bruno was imprisoned for seven years, before being excommunicated and burned at the stake by the Catholic church.
What crimes required Bruno's execution? He ridiculed the “mysteries and miracles” described in the Bible, claiming they were impossible. He put forward the astronomy developed by Copernicus, who said the earth and the other visible planets revolved around the sun, and that the stars could be other suns, with other planets revolving around them.
Galileo, who also put forward and further developed Copernican astronomy, publicly retracted his views in 1633, under the threat of torture by the Church. But Galileo knew that the Church and the rulers were wrong. As he was led from the court that convicted him, he is rumored to have said: “Well, it [the earth] moves, anyhow.”
In the beginning are the facts
To the feudal lords and the Church, what was most frightening about Copernicus, Bruno, and Galileo was their materialist approach. These early scientists all believed in God-they even dedicated their work to God. But they based their conclusions about nature on investigating material reality. Their “final authority” was nature.
But the feudal lords and the Church based their authority on the words in the Bible and in the writings of Aristotle. If Aristotle and, especially, the Bible could be proven wrong about nature by investigating facts, who knew where this could lead?  Would they go on to deny the existence of heaven and hell, and of the soul. Then what would keep people from rebelling?
The capitalists also fight against materialism. But where there is likeness there is also difference. The capitalist class had to use some materialist ideas to overthrow the authority of feudalism. For example, they had to oppose ''the divine right of kings.”
They also had to take a materialist approach to develop the science necessary for capitalist production. Aristotle and the Bible did not provide guidance for inventing steam engines or dynamite. Because capitalism is competitive, there is constant pressure to take a materialist approach in order to come up with techniques that will revolutionize production and produce more profits. Failure to do so often means defeat by other  capitalists.
Capitalists want science AND superstition
Once materialism was stalking the land in the form of physics, chemistry, geology, biology and engineering, what was to prevent the working class from using the same scientific approach to analyze and change human society? Science is a more powerful tool than superstition.
The capitalists panicked. They denied that the scientific method could be applied to history or society. The theories of Marx, Engels, and other advocates of dialectical materialism were attacked in articles and books by bought-and-paid-for professors all over Europe and America.
Marx and Engels were expelled from Germany, France, and Belgium. They lived in exile in England. Many of their comrades were jailed or killed.
In 1871, the working class of Paris dared to put some of the ideas of communism into practice. They established the first dictatorship of the proletariat- the Paris Commune.
The workers of Paris were furious with the Catholic priests for their service to the old regime, the bourgeois dictatorship headed by the “Emperor” Louis Napoleon, nephew of Napoleon Bonaparte. They removed the religious symbols from the churches, which they converted to meeting places for clubs of revolutionary workers. They took education out of the hands of the Church, where it had been placed by the old government, and put it in the hands of the Commune. Materialism, not idealism, was to be the basis of education. Ideas were to be questioned, not taken on faith.
Bosses build a  monument to their own fear
The Commune lasted only seven weeks. The revolution had taken place during the Franco-Prussian War. It was destroyed by a temporary alliance between the invading Prussian (German) army and the defeated army of the French bourgeoisie. The German rulers were afraid that revolutionary ideas would spread to Germany! So they rearmed their defeated enemies so that they could crush the revolutionary workers of Paris.
When the French capitalists recaptured Montmartre, one of the centers of communist strength, their troops rounded up and shot up to 50,000 men, women, and children. Their blood flowed down the sewers to the river Seine, which ran pink for days. Then, on the same hill where the Communards had kept their artillery, the Catholic Church built a white stone chapel called “the sepulcher of the expiation of the sins of the Paris Commune.” Known as Sacre-Coeur, it still stands today, a monument to the fear and hatred of the bosses toward workers who dared to overthrow the idealist lies of religion and apply science to society.
The battle between idealism and materialism is not an academic affair, but a vital part of the class struggle between workers and bosses for control of the world.