Which theories make sense to you? Try to think carefully about the myths of your own society (hard to do because they are your "sacred truths") and consider their social purpose.
Myths are symbolic ways of expressing understanding and beliefs, typically those regarding the universe or the beginning of mankind. Fantastical stories become myths as many naturally-occurring events could not be explained any other way in the ancient world, due to the basic, developing understanding of the natural world and much unexplained phenomena. Myths contain supernatural elements as the supernatural was the only way to explain these otherwise almost unbelievable stories.
Due to the importance of story-telling in all cultures, myths reveal elements of truth without necessarily referring to any specific person or event such as a legend would. Therefore, it would fall into "primitive science" as the natural events we understand today through science no longer have the mystery or remain unexplained or unexplainable. Interestingly, some myths exist across cultures, allowing for the possible conclusion that they are representative of that "collective consciousness" referred to in the question as, even before communication existed cross-culturally, these similar myths still existed.
Myths are certainly open to interpretation and their ability to "validate the social order" is seen in the way cultures use them to support superstitious or supernatural practices. They also explain what some see as unacceptable, allowing religions or cultures to perpetuate what, in the Western world, are offensive or completely objectionable beliefs. An example is the "caste" system in India which continues, based on myth.
In the modern era, we continue to use myths to explain those things we have yet to understand; for example, although the Moon and Mars do not hold the mystery they used to, we still do not know enough about life beyond the confines of the earth. It does make sense that the supernatural was blamed for many naturally-occurring events, especially weather-related ones, giving rise to many myths about thunder and lightning, rain and so on.
Evolution is a serious contentious issue in the modern day as it challenges the principles of The Creation and makes people uneasy. It also gives rise to a more secular society which creates its own set of difficulties. Christianity encourages compassion, faith and helping our fellow man whereas the secular society is often seen as being more selfish and lacking. Adam and Eve is a "sacred truth" and challenging that makes people uncomfortable. Accepting a middle ground and the concept that the seven days are more representative of seven ages or seven decades or certainly a period much more than seven days allows people to be comfortable with The Creation and with evolution, thereby allowing myths to have a place in every society. Myths allow those people who have no religious inclination to fit into a world where religion controls much action. The concept of good and evil - the source of many myths - does not need to be religious and shared beginnings do not then need to conflict in a secular versus religious society.