There are some very weak arguments:
- Of course, the founding fathers were religious (as it's being said at minute 3:00), including Jefferson. Thus their ethics were built on or supported by their religious beliefs. But from their European experiences they knew very well that interference of the state in religious matters would cause trouble.
What they knew is that there shouldn't be a state religion (i.e. like the Church of England). Not that there should actually be a "wall" or "separation" of church and state.
- At 3:39 he quotes O'Douglas that the American institutions presuppose a Supreme Being. I don't know whether this is still the view of Supreme Court judges today. Anyway, the illustration of a Christian church is just propaganda.
What the Constitution actually says, as written by those who actually wrote it, is what matters. Not necessarily what future judges think. I'm not sure what you mean by "the illustration of a Christian church is just propaganda," but this nation has always been a Christian nation in the sense that most of it's citizens have always been Christian.
And what do you do with atheists? Aren't they part of the American people?
Nobody is forcing them to believe or worship. But that doesn't mean they're free from being surrounded by religion or believing the false notion that there is a "wall" or "separation" between church and state.
- What does bad behavior in school have to do with decline of religion?
It's one example of the decline of mores in society, which has coincided with the decline in religious observance.
