If the Founding Fathers wanted the government to be able to show favoritism, they could well have done so.
The Constitution enumerates and limits the powers of the government. Nowhere does it give the the government the power to prefer one faith over another. You can say my interpretation is "modern," but you can't change that fact.
Why do you suppose the Founders didn't give any indication that the government has the power to endorse a religion, as you claim?
Who said endorse? It is wrong for the government to ban individuals from expressing their religious views, and that is what is being done today. The majority is being silence under the guise of offending some minority. That is not what our country was founded on.