“Politics as religion” is such a lazy argument because nobody has a definition of religion. It’s classic case of defining the obscure in terms of the more obscure. By any reasonable definition, a religion needs a transcendent being. Where is the transcendent being of this “secular religion”? You can’t just say the passion level is so high that it has passed into religious territory. That’s not how it works; the beliefs have to actually be structured like a religion, whatever that would mean.
The term “religion” does indeed have too many connotations. So let us not start there.
Instead, let us speak of a subset of culture that defines a tribe at large scale. A broad set of norms, symbols, beliefs and practices constitutes culture. Narrow that down to a subset of norms, symbols, beliefs and practices that clearly define who is or is not a member of the tribe. Focus on that subset. For example, Jews eat gefilte fish, observe Yom Kippur, and don’t pray to Jesus. But only a subset of those (observing Yom Kippur and not praying to Jesus) are tribally definitive. The rabbis won’t question your Jewish identity if you turn down gefilte fish.
No tribe is perfectly defined by a precise list of cultural characteristics. But bear with me and think in terms of tribally defining cultural subsets.
A tribally defining cultural subset will (a) tend to empower adherents to obey, enforce, and regularly re-affirm tribal norms, and (b) lead its members to fear and despise people who are not members of the tribe.
1. Cosmopolitans (including progressives, libertarians, and conservative intellectuals) would say that, yes, historically, “fear and despise” was part of religion, but that is a bug, not a feature. Ironically, cosmopolitans start to look like a tribe that fears and despises people who espouse traditional religions. And yes, there does seem to be a fourth axis here: cosmopolitan vs. populist, or Bobo vs. anti-Bobo.
2. The role of a transcendent being is to help motivate members to obey tribal norms, for fear of being punished by the transcendent being (See Ara Norenzayan’s Big Gods). However, belief in a transcendent being is not necessary to have a modern large-scale tribe. But it does seem necessary to have an out-group that you fear and despise.
3. Historically, major religions have usually fit my notion of a cultural subset that defines a large-scale tribe.
4. Usually, modern nation-states have fit this notion. There are those who say that nation-states were a better tribal bonding technology (so to speak) than belief in a transcendent being, and hence they made religion relatively unnecessary.
5. Finally, to the commenter’s point, I think that some political ideologies have come to fit my notion of a cultural subset that defines a large-scale tribe. The current progressive ideology seems to me to fit the notion particularly well. But the three-axis model suggests that conservatives and libertarians are tribal, also. Again, the emergence of the Bobo vs. anti-Bobo conflict has scrambled things quite a bit.