Of course liberalism/progressivism is a religion. Here is AJ Castellitto writing at American Thinker:
Some forms of political doctrine, for instance, function religiously, reflecting the worst features of orthodoxy and authoritarianism, especially when they sacrifice individuals on the altar of Utopian promises. Purely economic and political viewpoints, whether capitalist or communist, often function as religious and ideological dogma. Although humans undoubtedly need economic and political goals, they also need creative values by which to live. —Humanist Manifesto II
Theocracy can take various forms. Religious humanism is a fairly recent and particularly subtle theocratic development that has risen under the guise of secularism and religious neutrality.
Today man’s larger understanding of the universe, his scientific achievements, and deeper appreciation of brotherhood, have created a situation which requires a new statement of the means and purposes of religion. .. a vital, fearless, and frank religion capable of furnishing adequate social goals and personal satisfactions may appear to many people as a complete break with the past. While this age does owe a vast debt to the traditional religions, it is none the less obvious that any religion that can hope to be a synthesizing and dynamic force for today must be shaped for the needs of this age. – Humanistic Manifesto I
America was never a Christian nation represented by a single religious persuasion. However, our rule of law was definitely established under the ironclad premise that we are one nation under God!
The time has come for widespread recognition of the radical changes in religious beliefs throughout the modern world. The time is past for mere revision of traditional attitudes. Science and economic change have disrupted the old beliefs… In order that religious humanism may be better understood we… desire to make certain affirmations which we believe the facts of our contemporary life demonstrate. —Humanist Manifesto I
Read more: American Thinker