Personal Spirituality, irrationality without religion
The best you can gain from spirituality without religion may be a delusional view of reality, minus the traditional culture of indoctrination, you have another style, if still the voodoo of faith. Escaping the bastion of traditional religious organisations, with their rules and conformity, so you have free choice, exploration, and the ability to disagree massively, even if you cling to the mystical and experiential as critical for a serious view of reality. Religion minus the church, minus the priesthood, and without a holy book, it sounds superior to religion indoctrination, even though you still have groups and organisations, experts and officials, and, you have many books that offer spiritual knowledge. You may have broken free in some ways, yet you are still very much caged in others, the limits of an orthodox religion have been surpassed, but you cling to fun ideas that religious thinking can offer. 'Spirituality' is often just a term used to say personal religion, you mix and match based on what you wish, not what's traditional, nor what's evident, and commonly, its bias to own desires and the arguments you use to support your views.
The removal of Hell is an example of this with moderate Christians. Liberal Christians may rethink the concept, making it philosophical, non-literal, we see this process being watered down even more, which isn't a bad thing. Although most religions like to select texts, in new age spiritualism almost anything goes, and any nonsense will do. Such as the idea that Jesus spent time in India learning from great masters, at the feet of gurus, or even travelled to Tibet. Even though there is no serious evidence to confirm this idea in the least, you may as well suggest he moved to China while you're at it. This kind of thinking and that of moderates means the books are a starting point, how they proceed to include ideas depends on common sense. You can quickly dismiss a pet theory that is true but unknown and call a thing the true while not knowing that this is the case.
Many suggest a foundation to spirituality, so they kind God in all religions with a few wild interpretations. It's all selection, and who says what is the foundation and the errors created afterwards? Fundamentalists say their belief is right and the rest became corrupted, the spiritualists claim the cute stuff and then claim the unpleasant things are to do with negativity and materialism.
Even if many possibilities are used to say that the things you hold dear are correct, selection for fundamentalist Christians is to select stories about great floods in ancient times. Searching the history books and ancient legends to find anything that suggests that the biblical stories are true, and often finding a flood myth is enough for them to say that the global flood is reported in every culture.
To pose the idea that a global flood took place, even if their flood story is Atlantis, is simple enough. The way they prove the faith is by poor connections, so a spiritual person selects data to fit it into a lost global civilisation belief, and then without question will accept reincarnation stories as evidence, just because they have a bias the idea that one can reincarnate, as well as spirit channelling, and other mystic ideas.
Data selection based on bias includes the acceptance of hearsay and supportive ideas, which are held together by a unifying hypothesis, or series of hypotheses, and from the shaky ground the unsound idea is constructed. This can including the unaccounted years of Jesus meaning that he must have been in India learning from gurus, just as ignoring the periods of floods reported in various cultures and myths can seem to support a biblical view of a global event, well, if you are fine with selecting what you want, not that which is in full context and backed by solid evidence. And you may even say the great flood was evidence of the planetary shift that sank Atlantis, or even that it was the result of a near miss, as a planet X passed close to the earth, but you would still be trying to support beliefs with unsubstantiated legends.
The issue is how we rationalise things based on limited information, even using hearsay as evidence, so beyond myths, the concern is poor reasoning based on belief, a poor comprehension of terms and concepts, and this ignorance, and a kind of arrogance has a knock-on effect on society. Moderate people, whether religious or spiritual, are often very vulnerable to such leaps.