The notion of decadence, the eventual degeneration of a society or civilisation due to its own failings, once fascinated scholars. However, such a notion is now virtually unheard of except to some conservatives.
Interest in the idea of civilisational deterioration and collapse could have diminished because the idea was offensive to believers in the creed of perpetual social progress and development. Western campuses have, for a long time, been unfriendly to any idea that could align with reactionary rhetoric, such as a theory about moral decline, so most eminent thinkers in the West will avoid the topic completely.
Those of us most likely to talk about some form of civilisational decadence or moral deterioration gripping the developed and so-called "civilised" countries, namely the West, are likely to be of the reactionary mindset. This was not always the case.
There was a Marxist-Leninist notion of decadence, although it had no social or moral meaning and was only an economic observation. This was simply the theory that the epoch of capitalism could come to the end of its life, as capitalism could exhaust itself as a model of progress and from then on, only destroy its own accomplishments through war or turn into imperialism.
Civilisational longevity
In liberal and secular humanist thought, there seems to be no heed given to the longevity of one's culture or civilisation at all. All rational discourse is focused on the welfare, happiness and rights of individuals in the here and now. There is no thought for the morrow, as everything is invested in just doing what is right today. This is miraculously subverted when the issue of human survival is brought up. As soon as scientists suggest building settlements on Mars as a long-term investment against an extinction on Earth, the modern liberal is likely to support that endeavour, apparently forgetting that it does nothing for the welfare or rights of the individual.
People of the liberal persuasion are inhibited from investing in civilisational survival as any kind of priority, because it entails a kind of collectivism that could clash with individual rights. If investing in the distant future of humanity or our civilisation is made into any kind of priority, it could result in restrictions on behaviour that are offensive to individual liberty. It could, for example, result in social pressure to reproduce, which the liberal ideology prefers to treat as being solely the concern of the individual, not of the society or species.
It could be that a civilisation with a liberal monoculture could persist indefinitely, because it might gain traction with everyone on our planet, and hence there would be no threat from inside or outside. However, against a civilisation that has a sense of its own survival and longevity, a liberal civilisation may be an inadequate competitor.
While the Chinese civilisation could have a very strong awareness of itself and its needs, a liberal civilisation in the West may simply be a swarm of wandering individuals who are increasingly disparate, self-interested, and have no thought for whether their own civilisation could or should survive to tomorrow. Invariably, there will be those who will cry out now and claim that the Western liberal civilisation must be defiantly preserved and fought for, but is that not contrary to its own thesis, placing the focus on the individual's happiness? By being synonymous with liberalism, the West is unable to cast off its liberal preferences or put the civilisation's longevity ahead of the individual.
Cultural liberalism as decadence
Perhaps the granting of inordinate liberty to people is indeed decadence, a celebration of vice, which undermines the bonds that held society together and once made it anything worth fighting for. That is certainly what those of a conservative religious mind will tell us. There will always be those of that mind, and their greater moral certitude and reliance on a proven path of tradition may be a kind of inoculation against any peril that could originate from the excessive fixation on individual liberty.
The answer as to whether our current society or civilisation is destined for collapse due to moral decay cannot be asserted by me, but such a situation, even if real, may not be as troubling as it sounds. There are enough reasons to suspect some sort of civilisational collapse could occur, but it is unlikely to happen on a truly global scale or simultaneously in multiple countries.
Despite the globalisation, the world is actually becoming too fragmented for any kind of global failure of society and civilisation, and may even be too fragmented for a shared economic collapse. Countries and regions even within the West are taking quite different courses socially (the French and British approaches to how to manage cultural diversity, or the differences between individual US states on LGBT rights and birth control, for example, are very different).
If conservative worriers about a moral collapse are right, then, to use the metaphor of the Titanic, there is still reason to think the West is large enough and divided into enough compartments to stay afloat in some form. It won't be going down, in whole, even if the worst predictions of moral decay are valid.