This may be the lesson taught by the relative success of Mormonism in the modern environment. In The Mormon Culture of Salvation - a sociological study by Douglas J Davies (Professor in Religious Studies at Durham University, England; and not a Mormon) he highlights the exceptional success of the CJCLDS in inculcating and sustaining what could be termed certainty about the reality of post-mortal life.
I only get exposed to this at third hand, and superficially (not being baptised into LDS, nor having attended the Temple ceremonies, nor living the Mormon life) - but even thus remote and incomplete, the impression of a people who live in full expectation of eternity in Heaven is powerful and convincing.
As a culture we perhaps need more than any other single thing this kind of active belief. As well as being true - here are many factors about the full-on LDS life which support this perspective; but one neglected aspect is that Mormons also believe in pre-mortal life.
This is not unique to Mormonism, and there have been Christians who believe in pre-mortal life throughout history - some extremely eminent such as St Augustine - but in the CJCLDS it is right up front, and indeed one of the very first things taught to novices.
Belief in eternal post-mortal life is clearly essential to all Christians and always has been, while belief in pre-mortal eternal life is not essential. However, while not essential to salvation, (as well as being true) the belief in pre-mortal life has considerable advantages in making common-sense of belief in eternal post-mortal life.
It is very simple to imagine and to explain and understand the sequence of being pre-mortal spirit children of God; who voluntarily came to earth to be embodied and experience life as mortals; then die - when the spirit and body are separated; and finally be resurrected with spirit and body reunited for eternity with cleansed spirit and a perfected body.
It is easier to believe that mortality is an episode in our eternal life, than that our spirit popped into existence some (uncertain but precise) time in the womb then lived forever from that point forwards.
If it is indeed true that modern Man needs first and foremost to believe in his own eternal life (and also the eternal life of anybody and everybody who chooses eternal life and is prepared to live accordingly) - then a wider awareness of our pre-mortal existence may be extremely important.
I don't think it would be hard to convince most people of this - since so many people have an intuition and some cloudy memories of their own pre-mortal heavenly existence, what is needed would be more in the nature of of a reminder and a validation of something they already sort-of know.