Organized religion is a package of beliefs and behaviors that have been honed over tens of thousands of years to provide people with things they need both psychologically and socially. Until recently religious behavior couldn't really have been separated from the rest of tradition and society. It was one "package". Having all of these things wrapped up in one package makes it easier to teach and train people to follow good ideas, like "don't eat food that spoils quickly" and "don't spread STDs with promiscuous sex". Now that we have better understand of which behaviors are helpful we may not need all of the extra baggage that traditionally came with religion. But where is the new "package" of useful behaviors to replace the old ones? Often if you discard religious tradition you also discard good guidelines for living, and instead rely on random trends or worse profit-motive marketing for your guidelines.
I suspect religious people will get angry at this line of reasoning, thinking I am missing the entire "point" of religion. From one point of view I am discounting the whole purpose of their religion. But regardless of the supernatural truths of the universe, it is certainly true that religions carry a great deal of traditions and guidelines for living beyond the purely spiritual.