The basic problem is that we have allowed theism to co-opt the language and much of the universalist ethic of humanism. Theism in its ancient, tribal form is a particularist phenomenon, aimed at fortifying a small portion of humanity in its competition with other small human groups. In fact, the closest things we have to old-time theologians in our modern society are the astronomers, searching for first origins, and the underlying principles of the cosmos. I submit that humanity has embraced at least some humanistic ideas and ideals for quite a long time. In our time, science and a humanist view of the essential unity of all people have largely replaced theism as organizing principles on which educated people base their understanding of their world and the cosmos.
Many people still think of themselves as theists but are in fact closet humanists.
They continue to belong to one or another of the established denominations, but only because they were brought up that way as children. Their ethics and values are almost entirely humanist. It is humanism, not theism, that evokes their concern about starvation in Africa, and makes them ashamed of the fact we still have not completely eliminated race prejudice from our society. It is humanism, not theism, that makes them want to preserve the planetary support system for future generations. In the context of contemporary conditions it is humanism, not theism, that has a lock on the values and ethics that humanity needs if it is to progress, indeed if it is even to survive.