Telika: Secular maggots coopt history and munch on "hero" corpses just the same, making them symbolic figures of this and that, sacralizing them their own way, and planting their flags on them.
While I understand what you are trying to get at, and agree with some of your core reasoning about the commonality of root causation of affect, I think it's also seductive to overapply reductive parallelism between discrete magisteria.
Since systems like religion and secularism both come out humans, naturally there will be manifestations in each that are driven by the same causes. So it is easy to point to both and say "see, here one does X and the other does Y, naming them different but at heart being the same". But this is also facile if one doesn't consider the multifarious layers that go into those manifestations. This is where reductionism leads to oversimplification.
In terms of sociodynamics, I would say that the overarching difference between secularism and religion is that the former strives for universality, whereas the latter strives for segregation. Secularism is about seeing where we overlap and finding what we all want as humans. Religion, conversely, is about binary absolutes - the believer versus the doubter, the obedient versus the heretic, the saved versus the damned.
If you prefer, you can view secularism as striving for the minimal set, the baseline for what we must do as a society to ensure that individual rights and freedoms are honoured. Conversely religion strives for the maximal set, an orthodoxy of what every individual must believe, and must not believe, in order to ensure stricture. Secularism embraces heterogeneity, whereas religion espouses homogeneity.
A thought experiment that I often return to helps delineate this primary contrast: If we all woke up tomorrow as secular humanists, by the end of the day we'd all still be secular humanists. But if we all woke up tomorrow with the same religion, by the end of the day we'd have splintered into dozens of new sects. Because the former is predicated on where we are alike, and the latter on where we differ.