Religion is primarily based on fear, particularly, fear of the unknown as well as greed and ego. When winds blew violently and caused devastation, our primitive forefathers started worshiping the wind as God and assigned a stone to represent wind god.
Similarly when rains caused flood and brought havoc, our primitive forefathers started worshiping rain God and assigned a stone to it. Thus all the natural powers like fire, rivers, oceans, etc. became God and were assigned carved or uncarved stoned to represent them. Then there were certain super-natural forces like volcanoes and they too were worshiped.
Meanwhile man who was a hunter became an agriculturist and artisan as well as a traders. So, he started worshiping the goddess of wealth and because of his greed, he started worshiping every power which gave him benefit like Sun, Moon, etc.
These gods were now given human shapes and other shapes and placed in temples to be worshiped by all. These temples were managed by priestly class which was very clever and intelligent. Meanwhile certain powerful people emerged as leaders of men in their respective areas and started ruling the people. They sought the help of the priestly class in declaring their divine right to rule.
Meanwhile some of the priestly class people who were more intelligent than even the rulers thought of a Creator who must have created all the powers which were called god. So, this Creator was called God with a capital G.
Meanwhile rulers were fighting amongst each other to capture more territory and seeking the blessing of various gods through the priests. These battles took up the life of a number of people who were reluctant to die. To create Martyrs, priestly class came up with the idea of heavens.
They opined that those who were Martyred in the cause of the King or their respective religions, would go to heaven where they would have the company of menses less fairies having scented sweat, gay slaves, and wine to drink and honey to eat. Thus many Martyrs were prepared to die for the King and the religion by clever priests.
The various religions found by rival priests who formed various hierarchies with each hierarchy headed by a so called Prophet or Incarnation of God on earth, fought amongst themselves and killed so many people.
Coming to the modern times, Hitler killed 6 million people because they belonged to a particular religion caused Judaism. In the partition of this country, 1 million were killed because of their religion. So, say no to religion and yes to atheism and agnosticism.
This is also necessary because religion spreads superstitions through rituals, astrologers and palmists with the latter providing doubtful solutions to the problems of the concerned individuals in lieu of offerings made in cash and kind.