What a great question.
I think the world we live in is incredibly complex, and that it's possible for people to adhere to tenets from many religious traditions. Gone are the days when everyone you knew or lived near believed what you believe, or when there was one dominant worldview. However, some religions may cross-pollinate better than others.
I bristle when anyone finishes the sentence, “all religions teach … ” It seems to me that strains of religious iterations pop up in different places in the world, and different times, to meet the needs and desires of the people. They are celebrated, hated, and/or discarded. When new information is discovered, theology has to catch up to it, and integrate it somehow. For example, the different heresies (from the Greek, meaning “choice”) in the Christian tradition, The Albagensians, the Cathars, the Waldensians, the Humanists… what they lifted up eventually became absorbed into the Catholic traditions.
Not unlike travellers in the Old Testament, who paid homage to the local gods, modern travellers have the opportunity to learn so much about local traditions and religious tenets, and to practice what they find in far away places.
Too often, what this syncretic panoply boils down to, is what I like to call “The Salad Bar Approach” to religion: take this, leave that. A person (or a culture) can wind up with wild abstractions, without community and discipline to encourage them to live a better life together.
