You're not wrong about the Evangelical Right per se, but their irreligious opponents have always been guilty of the same sin.
I've seen arguments that dogmatic secular modernity came first and produced conservative religious fundamentalism as a reaction to it, but I suspect they grew together, like two sides of the same coin.
Separation of church and state neither means that America is an officially Christian nation nor that the opponents of religion are specially privileged to use the state to lessen the role of religion in society via the education system or other state-funded channels of influence. Secularism means governmental neutrality in questions of or pertaining to religion. Both sides have refused to acknowledge the limitations placed upon them by the constitution, and if the Evangelical right really kicked off in the 1970s then chronologically speaking it was the irreligious who were the first to cross that line.
Two groups that define themselves in terms of opposition, result in two groups that taken by themselves, are inexplicable within the context of their respective positions and which represent these two “polar opposites” categories of one and the same movement
To say that opposites are “polar” is to say that they aren't just opposed or separated; it is to say that they constitute a whole, there is a reciprocal, transactional relationship being described. Despite being opposed, they are closer together than either of them is with the reasonable, middle view.
On one side of this polarity is an excessively dogmatic secular modernism that doesn’t appear to be true to science, and on the other side of the coin, it is opposed by a dogmatic religious fundamentalism that doesn’t appear to be true to Jesus.
(And as an aside, the Establishment Clause only applied to the Federal government until the 1940s.)
I Googled to see what you were talking about, very interesting, never occurred to me it wasn't a principle that always applied to all levels of government. Good thing the Supremes made that ruling I guess, or I'd probably live in the Baptist State of Georgia right now.