The Trekkies never believed in Star Trek as the literal truth, although that concept was explored in the 1999 movie "Galaxy Quest". However, they do believe that the actors themselves existed, and the stories told about them, such as Lt. Uhura being asked in person by Dr. Martin Luther King Jr. to remain on in her role as communications officer after the first season. http://en.wikipedia.org/wiki/Uhura
Star Trek was the first TV show in America to feature a black woman as anything other than a maid, and the first to show an interracial kiss. And it's message was liberal and multicultural in many other ways.
Like the Bible, Star Trek has a canon that has grown around it, comprising all the known information about their universe. Even things that were not revealed in the original series. For example, Lt. Uhura's first name. Or the blueprint plans of the starship Enterprise. Or the complete lexicon of the Klingon language.
Star Trek presented a philosophy, a vision of the future, and a moral code. All were based on science and reason rather than magic and superstition. The positive message of the program was hope for the future of all mankind. This was explored through many episodes depicting variations this vision of the future.
The future vision of Star Trek can be summed up as this. Humans discover space travel, and begin exploring space, moving Earth colonists onto an infinite number of new uninhabited, but habitable planets. There are other non-human planets with intelligent life already, some primitive, which are left unharmed (hopefully) after a scientific investigation. Others are hostile, and advanced technologically, and are a direct threat to Earth's Federation of planets. For example, the Romulan and Klingon empires.
Star Trek was introduced just a few years before man finally stepped on to another planet, and Star Trek's vision of the future assumed that man would achieve true space travel. At the time of the original show, it did not seem so impossible, but soon after landing on the moon it became apparent that the human race was at least a thousand years away from travel to other stars. Soon after, a new philosophy had to replace the "space travel" idea. It seemed that the only way to ever achieve space travel was to first ensure that the planet Earth was not destroyed, giving us time to develop this new technology. The idea developed that we were already travelling through space on a ship called "Earth", and we needed to treat it like a space ship, meaning to keep it from being polluted and make sure we don't run out of fuel until we reach a refueling station or discover independent space travel.
The Star Trek moral code was just as important as its vision for the future. It started with the acceptance of different races as equals, and with all countries being part of a united world government. This would bring peace to Earth, and was the best way for Earth to move forward into space exploration.
A second part of the Star Trek moral code was stated in the Prime Directive.
That there would be no interference with any civilization that had not discovered interstellar travel. This of course was a reference to neither colonizing nor exploiting primitive civilizations.
By examining many other episodes, it is quite easy to fill in the rest of the moral code for Star Trek. Do not attack anyone who has not attacked you. And if they are a primitive civilization, do not strike back, simply retreat. No torturing prisoners. No brutal punishments, no revenge. Actually seems more or less in keeping with a peaceful version of either Christianity or some other Earth religion, with the superstition and supernatural removed.
Of all the episodes of Star Trek, I do not remember one where there was any terrorist attack on the Federation of planets. I don't think that this was because the writers had not thought of it. Terrorism was inconsistent with the rules of Star Trek. In Star Trek, those who would do you harm have giant space warships, and know how to use them. If they do not have space travel, then they stay home, protected by the prime directive, and have no reason to hate you because they don't even know you exist. You might say that terrorism comes about because you ignore the Prime Directive. It is the result of exploiting and interfering with primitive cultures. I don't remember terrorism being an issue when our enemies were Germany, Japan, or the USSR.
Was Star Trek an example of Moral Relativism? I guess its debatable. In the case of primitive cultures, it was quite clear. No missionaries were sent down to tell the people their culture was evil. That was an example of Star Trek's Moral Relativism - morality is relative to the culture, not to be judged evil by another culture. In the advanced cultures of Kilingons and Romulans, there were no missionaries either, as they would have been quickly slaughtered. The contrast in morals was obvious, though never put into words. The Federation was not out for war and conquest, while their enemies were.
Within the crew of the Enterprise, there was little chance to explore moral relativism. All the crew members were loyal and seemed to have the same values, regardless of their race or country of origin. The misfit was Spock, a Vulcan who was half-human. But even there his relative difference was mostly in use of self-control and logic rather than violence and emotion.
The Ethics of Star Trek, from http://memory-alpha.org/wiki/User:Ottens/Phase_II
"Gene Roddenberry, a man who was very open-minded about the customs of different cultures, said: "[By the 23rd century, we] will have learned to take a delight in the essential differences between men and between cultures. [We] will learn that differences and attitudes are delight, part of life's exciting variety, not something to fear". Roddenberry certainly must have supported cultural relativism, which, according to James Rachels, a contemporary American ethicist, is a theory that makes six basic claims:
1. Different societies have different moral codes.
2. There is no objective standard that can be used to judge one societal code better than another.
3. The moral code of our own society has no special status; it is merely one among many.
4. There is no "universal truth" in ethics - that is, there are no moral truths that hold for all people at all times.
5. The moral code of a society determines what is right within that society; that is, if the moral code of a society says that a certain action is right, then that action is right, at least within that society.
6. It is mere arrogance for us to try to judge the conduct of other peoples. We should adopt an attitude of tolerance toward the practices of other cultures."
Picture: Mr. Spock. Half human, half Vulcan I consider him to the real moral leader and inspiration despite his status as second in command to Captain Kirk.