When referring to the “Separation” issue, you must remember what the Founders had just escaped.
In England, the Government and the Church of England are intertwined. The British Monarch IS the Head of their Church.
The Founders wanted no part of this concept in their new country and took steps to prevent it by preventing the government from establishing a religious body.
More people should know history.
Yes, the use of the term “establishment” is important here. It does not mean “setting up” (e.g. “establishing a colony at XYZ”). After all, in 1776 most of the major religions we know already existed. It means incorporating a religious body into the government and laws, essentially nominating a state religion. In Britain today there is a movement known as Disestablishmentarianism, their goal is to separate the bodies of Church and State. And a spin off is the longest word in the English language, antidisestablishmentarianism.