Religion is more than just proselytizing an idea (whether it is about a god or something else). The way you appear to want to define it, any movement that actively seeks to convince people it offers the best option for a given scenario (best political rule, best sports team, best way to educate and train, etc.) is the equivalent of a religion.
Not just when you think or advocate that an idea about any matter is best but when it involves how you think people or society not only should but must act (and again, with all alternatives are seen as invalid).
If people truly worship their political leaders and otherwise feel they should be treated as gods, even while admitting they didn't create the universe, why shouldn't that be regarded as a creator-less religion (especially if they feel the question of a universe creator is irrelevant)?