Ancient Confession Found: 'We Invented Jesus Christ'

[Sword of Christ]

So it couldn't have been decided by the founding fathers that they simply wanted to set-up a secular state

I'm not saying they were deliberately following Christs teachings but they still came from a Christian culture, post reformation era. Had they come from an Islamic culture you can be sure things would have been a little different. Christianity is fully secular society friendly there's no theocratic political agenda inherent within it, all that had to be bolted on as something extra. If you want to see what Jesus had to say about ruling elitist religious authorities you can read it for yourself.

- regardless of what any given religion said, notwithstanding Jesus support for a fascist dictatorship?

The only thing Jesus supported was God and humanities relationship with God through himself, he didn't support any human political or theocratic systems. By maintaining the separation of Church and state the US has set something up that would be closer to the ideal of what he taught. It necessarily a more "atheistic" foundation as it leaves people free worship God as they wish, and under these conditions Christianity has thrived away. If you want to stifle Christianity then state run churches such as those in Europe seem to do the job.