Well-- one might say that Judaism or Islam, Hinduism or the Jains, Rastafaria or the Animists are not attempting to interfere in the political process by leaning on their congregations because they know that the congregation won't accept being leaned on by any of them.
If that were not the case history shows that they would lean for all they are worth. Setanta's argument is nonsensical and relies on little or no attention being brought to bear on it. Which is to say he thinks we are all stupid. The up-thumber being a case in point.
The problem with the decline of Christianity is what it declines into. The tyranny of the reason, thought by some historians to have been the preface to the decline of Classical culture, is bound over time to result in smaller, narrower and more and more unfruitful investigations. Witness the search for fossils and the contradictory conclusions drawn from them as investigators pursue allocations of funds rather than any real science with the sole objective of making a name for themselves. Also photographs of more and more distant objects in space and smaller units of time after the Big Bang.
Setanta and his cohorts will never venture into the territory of what will the decline of Christianity lead to. And such a decline is destined to lead somewhere.
I suggest that it is his Christian consciousness which underlies his reticence in that important regard.
He is rather similar to a street furniture vandal who pays no mind to the obvious possibility of the US having 308 million street furniture vandals. He makes the crass error of comparing something that exists in reality with some abstract, ideal state which does not exist and can possibly never exist.