Leaving aside whomever they "they" are or whatever conspiracy might be ongoing let's just make things simple and reality based.

You are certainly able to erect whatever symbol you want on private property  and worship whatever and however you want - within the usual caveats. So can I. We may believe each has the only right way of doing things  even if each is totally different or diametrically opposed to the other.

What you or I cannot do is attempt to make others worship or participate as either of us claim appropriate. And neither of us can claim the general public must be coerced to follow either of our very different practices and views. Since public spaces belong to the entire public a single organized religious sect ,  regardless of how large or how fervent adherents may be, cannot exclude others or control public behavior.

The Establishment Clause is not solely about religion. It addresses the traditional mechanisms of social control  inherent in organized religion. Something the founders well understood if we can trust what they wrote and we tend to ignore.

There is no grand conspiracy at work. Citizens are at liberty to practice as they choose and cannot force others to do the same.  That includes ALL Citizens not just those who happen to agree.

The argument you make Moe is overly selective and misleading. As for the interpretation of "original intent" that is an interpretation at odds with historical record albeit on favored by some Citizens. But opinions vary.

A more complete reading of the separation clause reveals the idea that government may not establish religion which was a very serious problem and the genesis of the Enlightenment period. A history the founders were very much aware of. Emphasizing only a few words out of context may seem convincing but is pretty transparent evey time.

There is no prohibition to display biblical injunctions on private property. Happens all the time. Using public property to proselytize however, is exactly the thing the separation clause addresses.

 And again, as a card carrying academic you are mixing a little fact with allot of conjecture, the Separation Clause does in fact bar the government from establishing a national religion such as the Church of England as it should, but freedom to practice doesn't limit citizens from setting up a Christmas Tree or a Nativity scene or Menorah in a Community park,   
i happen to agree with( to paraphrase) Thomas Jefferson - It matters not whether a man believes in many gods or none it neither picks my pocket nor breaks my leg.

You are, of course, at liberty to believe as you wish and practice religion as you choose, with the usual caveats. We all are thankfully.  What you or I cannot theoretically do is require others to believe as we prefer.

Seems reasonable.

Now Moe I'm sure you know you're overstating the case, as usual. While the comment may reflect a belief that does not make it fact, which it indeed is not.

Fortunately freedom OF religion is also taken to mean freedom FROM religion  A safeguard vitally important in a democratically organized society as our founders well understood.

I favor the observation by Herodotus: "All men are equally knowledgeable about the divine."  seems like a reasonable operating principle

Seems so ....

Today is also National Religious Freedom Day. An observance that has a much longer history in our nation.