Religion has the great advantage of being practiced in community. It may not have the pure wisdom of Seneca, but what good it can offer is more likely to stick.
Unfortunately, the Christian community offers more social capital than the Stoic or the atheist in the west.
Fr. Alphonsus Rodriguez, S.J.[1] (d. 1616) has sometimes been called a "Christian Seneca".[2]
I had never heard of him or his major work "Practice of Perfection and Christian Virtues" until 2004, when someone I met on a retreat recommended that I hunt down a copy of Joseph Rickaby's[3] masterful translation from the original Spanish.[4][5]
I had the opportunity to read through "PPCV" over the period of about a year back in 2007-2008, and I can only say that it leaves a remarkable and lasting impression. I would think his treatises on humility, examination of conscience, and mental prayer (meditation) would be of great interest even to those who aren't particularly religious -- i.e. the practical wisdom contained therein is like a toolkit for coming to "know oneself" for true.
Sure. If you want to be a politician in the West, you can't really avoid participating in a Christian community of one kind or another. But people who are interested in stoicism probably have other goals.
It isn't true of Ireland, Britain, Australia or New Zealand. I don't think it's true of Canada. Among WEIRD [0] nations I think the US is the only one where being openly atheistic would abort any serious political career.
According to a 2012 Gallup poll, 43% of Americans would not vote for a qualified atheist candidate. For comparison, the numbers for a Muslim candidate or a gay or lesbian candidate were 40% and 30%, respectively.
While being an atheist won't sink you, being christian certainly helps in Australia. For example, John Howard was fond of recording video messages which would get played in christian churches during the service.
My guess is that it would be more helpful at a local than a national level, but church influence could definitely swing a few key seats.
As a counter-example, everyone in Australia knows that our Prime Minister is at least agnostic. It might well be a point in her favor, to the very slight extent that people care.
Now if only they would stop censoring the Internet and using the same citizen monitoring that the Chinese do it might count for something.
The west is obsessed with religion, as has been pointed out, however hypocritical it might be it's a well practiced ritual in DC if you want to get elected for anything.
Unfortunately, the Christian community offers more social capital than the Stoic or the atheist in the west.