What's The Deal With Dark Matter?

Although much is known about the universe, many questions are still left unanswered despite the advances made by scientists everyday. The Big Bang Model tells us how the universe began, Einstein's General Relativity tells us about the relationship between space and time, and our telescopes can see almost all of the visible universe. However, as I read about in Simon Singh's Big Bang, the science community cannot prove the existence of what is known as dark matter. Stars at the edges of galaxies like the Milky Way are observed to maintain their orbits. They are kept in their orbits by some force that astronomers and physicists struggle to determine. Cosmologists believe that there must be vast quantities of 'dark matter' in all galaxies, dark matter being matter that does not shine but which exerts enough of a gravitational pull to keep stars in their orbits. Although no dark matter has ever been found, scientists believe that it must make up a majority of the universe. How has this idea become  accepted in a community that relies on observations and solid proof? I honestly don't know enough about the topic to answer that. I read an article in the July/August 2015 edition of Discover magazine in which a scientist created a theory called MOND that would explain the orbits of such stars in terms of gravity in extreme environments. Whereas Einstein's General Relativity describes extremely high gravity environments and Newton's laws describes environments with gravity similar to that of the Earth, MOND describes extremely low gravity environments. I don't entirely understand what MOND is, but I am open to all theories.  Learning from past scientists who refused to consider the Big Bang model of the universe, I want to try to think of all possibilities until solid proof points toward one more than the other. Although no scientist myself, I think the main idea from the whole Big Bang v. Steady State debate is to be open to all ideas because once evidence is found, we have no idea which theory (if any) it will support.

The Paradoxicality