Let's run with this a little longer as both Scott (Gray) and Neil (OSO) think I'm being unfair to humanists.
Firstly, I'm not aware of any theoretical reason why a humanist culture is necessarily incapable of sustaining long term moral endeavour and improvement. My concern is a practical one, ie that I'm not aware of this sustaining being done in this culture. ("This culture" mainly referring to the UK, but not excluding the other Anglo-Saxon societies).
Secondly, this point is one about religious belief over against secular thought. In other words it isn't something that hangs on the specific beliefs advocated by Christianity. Confucianism, for example, is more than adequate to foster the social goods that concern me, and the theologies of Christianity and Confucianism (if the latter could be said to have a theology!) are very distinct.
Thirdly the existence of humanists who do good things is insufficient to answer my concern. We can all agree on the existence of such wonderful people; conversely we can also agree on the existence of wicked people who happen to be religious believers. The question is about what fosters the goodness and inhibits or reforms the badness.
Fourthly, this is a separate point to the one of accountability (hence a separate post). Whether humanism can coherently give an account of its accountability is to my mind an open question (I'm pretty sure it can't) but that's not the concern here.
The issue is this: the mainstream of Christianity demonstrably cultivates the virtues, be they compassion, a desire for social justice, a commitment to the truth, and so on. These virtues are developed through the adoption of particular practices which embody them, and cohere through the telling of stories and sharing of expertise. There are institutions which exist to, amongst other things, foster this moral development. In Christian terms it is called discipleship; doubtless there are equivalent terms in the other religious faiths.
My point is that I am not aware of institutions which cultivate the development and amplification of a moral sense, with associated practices and disciplines, within this country, of a humanistic form. I repeat, such things are not at all impossible. They seem to have existed in Ancient Greece (the gymnasia). I just want to know - where are they? (It's also perfectly possible that there are many such institutions, and this post is merely parading my ignorance of them).
Hence my comment in the original post, that humanism is drawing on the bank balance built up by centuries of Christian teaching. I want to know where humanism is putting money in.
(For those familiar with him, the influence of Alasdair MacIntyre should be obvious!)