The concept of being spiritual but not religious suffers from a lot of confusion. One reason is that spirituality fails to elucidate specific guidelines on how to "do it right." Unlike religion, which often errs on the other side with too many rules, or too rigid of rules, a generalized spirituality offers few or no standards for behavior, or even for thought. Many who have turned to being spiritual but not religious left religion in the first place to escape overly rigid rules, so they like it this way.
But having no explicit guidelines at all can leave seekers prey to superficial and spiritually counterfeit ideas. You can't expect your life to improve because you suddenly start wearing crystals, for example. You can't come from a chaotic and unregulated lifestyle and claim an enhanced spirituality because you have had some type of supernatural experience. This absence of guidelines and structure unfortunately leaves people confused, and actually harms the movement -- to the extent there is a "spiritual but not religious" movement. It confuses and misleads would-be spiritual but not religious people by luring them into superficial interpretations. But it also gives authentically spiritual people a bad name. It allows others to lump any spiritual person who doesn't follow a particular religion into the category of "flakes" and people with "poor reality testing skills."
An understanding of the spiritual development stages begins to provide a much needed structure to spirituality, and that can orient people toward an authentic spirituality based on a more solid form of personal responsibility, and a deeper form of interpersonal integrity than even our religions teach.
One example of this is the concept of inclusion versus exclusion. At the literal level, our religions teach specific beliefs that differ greatly from one religion to another. This leads to each religion insisting its own teachings are more right than all the others. It gives the adherents a sense of superiority, and makes them feel they must convert others to that religion. This causes a sense of competition and discord between the religions. Each religion excludes outsiders, and denies their beliefs have any validity.
But the spiritual development stages tell us we need to move beyond these literal beliefs to become spiritually mature. The process includes a step where a person thinks through what he or she has been taught in an open-ended critical manner. This may lead her to reason herself out of belief in that religion, or at least it will lead her to grasp the same teachings in a less rigid, and hopefully less literal, way. Following that process to its extreme end, we can see that once we maximally loosen our religious interpretations, most religions can be seen to have been formed on common "goodness" values on which people from all cultures would agree. The various religions therefore are but localized and literalized interpretations of these values.
At the upper spiritual development levels, a person can see that all religious traditions have validity when their teachings are seen as metaphors for more universal truths. Spiritual people can hold these same values just as well without a religious basis, without any religious beliefs.
Once a person accepts this, they no longer need to exclude those who don't share the same beliefs. They can begin to include more -- or even all -- people into their same common humanity. They are no longer primarily a Christian, a Muslim or a Jew, but a member of a much larger group -- all humans, or in the fullest expressions -- all of creation -- to include animals, rocks, the environment, and even the unseen reality. In this way they begin to approach a form of spirituality that imposes a sense of personal responsibility toward all beings, and toward the entire universe. Unlike the specific religions, which exclude outsiders, this form of spirituality includes everyone and everything.
To what percentage of the universe does our personal responsibility extend? Toward whom do we feel we must act with greatest integrity? How much can we include in our circle of concern? This is one criterion of mature spirituality that transcends the individual religions -- one means by which a person may judge their progress along the spiritual path. It is a path a can be followed from within a religion, or from outside of it, by the spiritual but not religious, and even by those who deny both religion and spirituality. Greater truth, and greater maturity, is found beyond the religions that exclude, and found within forms of spirituality, religion or even nonbelief that find their basis in inclusiveness.