As a note: I haven't read those humanist manifestos...
Everything that I have read from Biblical Christians (who critics call conservative,uninformed, and in a realm of fantasy versus reality) indicates that the world will by and large reject all forms of organized religion due to the fundamentalist oppressive nature of its tenets and will embrace a form of belief in the human animal and our collective potential known as secular humanism.
Many of us don't see this as a problem. Organized religion has led to immense problems over the past few thousand years. There is no evidence those problems are lessening either.
What does the evidence show us regarding international relations, global finance, the steady decline of the United States both morally and financially, and the rise of false religion the world over?
Are the two related? It is not uncommon for civilizations to rise and fall, and the declines we are seeing are not unprecedented in history. Why would you consider linking this to some form of religion instead of other factors, such as multiculturalism or the decline of nationalism, or just the aging of a civilization? You know the saying, "Its hard to have a decent parade when everyone is dancing to a different drummer." That seems to be what this country is experiencing.
Are the secular humanists right? Is religion and ancient beliefs threatening a logical and rational future for our planet and ourselves?
Religion and ancient beliefs are based on -- beliefs. Beliefs are the opposite of facts and evidence and rationality. As Heinlein noted,
What are the facts? Again and again and again—what are the facts? Shun wishful thinking, ignore divine revelation, forget what "the stars foretell," avoid opinion, care not what the neighbors think, never mind the unguessable "verdict of history"; what are the facts, and to how many decimal places? You pilot always into an unknown future; facts are your single clue. Get the facts!
Or are the Christian literalists right? Are we all doomed to a bleak future by our actions of rejecting God and seeking to deify ourselves as the ultimate source of wisdom and logic?
Rejecting god? There are tens of thousands of different christian sects and denominations alone, as well as many thousands of different religions and who knows how many different gods, back in history as well as now. Why so many? Simple: religions and deities are all based on belief, and when there is a disagreement you see a schism rather than using evidence to settle those differences. Religions can't use evidence! They are relying on unevidenced beliefs.
And you want to trust humankind's future to that nonsense?
Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
Belief gets in the way of learning--Robert A. Heinlein
In the name of diversity, college student demands to be kept in ignorance of the culture that made diversity a value--StultisTheFool
It's not what we don't know that hurts, it's what we know that ain't so--Will Rogers
If I am entitled to something, someone else is obliged to pay--Jerry Pournelle
If a religion's teachings are true, then it should have nothing to fear from science...--dwise1
"Multiculturalism" demands that the US be tolerant of everything except its own past, culture, traditions, and identity.