Note: The following may appear offensive to religious people. I prefer people that would read religion contradicting opinions and ideas and not get offended but I will still warn those people who do.
I believe religion was created as a purpose on having an explanation for the unexplainable. Many years ago when most religions where formed people had no idea how things worked. In recent scientific times religion has started to fade away and little has been added to them as logical explanations have been given. Today in rainforest's tribes still create religions because there is no explanation. They use creativity to answer mysteries of the universe. For example I heard a tribe in the Brazilian rainforest use airplanes as a form of their gods. Of course this is false and my point is people will make up anything to explain is they have the desire to do so.
My next point against religion is that there are many. Not all can exist and be true. Also single religions tend to stay with certain nationalities meaning each religion was made separate and as each is different they must be invalid.
So why do people believe in religions still? There are a few reasons why:
1. People believe what their friends and family believe from out of date beliefs that pass down this way.
2. People feel comfortable to believe there is a god/gods to help them or that there is an afterlife.
3. People go to religion for help with problems that may occur.
4. An extra-ordinary occurrence could point a person into religion while it could be easily explained otherwise
5. People do not understand how things work so they exaggerate or create stories in which they are able to base religion on. A good example is rain forest tribes.
I think number 1 is the biggest cause as people are brought up by families into religion.
Believe what you want. However please accept other peoples opinions and do not think you have any more rights than other people due to your beliefs. The biggest problem with religion is the conflicts. I'm hoping within the next 100 years religion will die out completely along with the conflicts that cause so many wars and so much terror.