The utopian project to make Heaven on Earth reached its zenith in the middle 20th century with the triumph of Communism in many nations; but has never been officially or explicitly abandoned - and in a covert and incoherent fashion still motivates the political Left (which now rules the world; sometimes operating under other such flimsy disguises as conservatism, republicanism, capitalism etc.).
The contrast drawn is between - on the one hand - Christianity which offers resurrected eternal life in Heaven - only attainable on the other side of that transformation that is biological death (aka. 'pie in the sky'). And on the other hand; mainstream, materialistic socio-political Western ideology; amplified by the promises of transhumanistic technologies, which offers a positively transformed Heaven on Earth.
Of course, any such thing is currently blocked by the inevitability of disease, ageing and death and the limitations of human intelligence and emotions. Also the inevitability of suffering.
But (so the utopian hopes go) assuming these can be cured by (waving of hands at this point...) advances in technology (drug progress, genetic engineering, computer-brain interfaces... whatever); then why wait for something as uncertain as Heaven-beyond-Death when we can have Heaven-Now?
All assuming that humans can live forever, without ageing or disease; without suffering or misery (unless they want it; and then only as much as they want for as long as they want) - and with as much happiness and pleasure as they desire. Potentially a life of bliss...
Who wouldn't want that?
And even if Christians can have Heaven after death - what about everybody else?
What about those (presumably a vast majority) who do not want to follow Jesus; including those who do not believe Jesus, who hate Jesus; who are bored, indifferent or hostile to Christian ideas of Heaven - especially if these require onerous restrictions on lifestyle (especially sexual expression)?
Assuming it is achievable; a techno-Leftist utopia promises a Heaven for everybody! And here and now and for-sure.
That is the special appeal of Heaven on Earth; that is why so many people regard HoE as morally superior to the Christian Heaven.
Universal happiness forever... Better by far, yes?
Not better, but in fact Hell on Earth, rather than Heaven.
But why so?
Leaving aside issues of feasibility (and I do not believe it is possible to do these things - indeed I anticipate a continuation of the already-happening collapse in human capability) there is a basic reason why Heaven on Earth is actually Hell; and that is that any actual Heaven on Earth must be based on compulsion.
Why? Because Heaven on Earth is only possible with universal cooperation.
It would not be Heaven if people were free to exploit, parasitise, destroy, foment discontent; and from everything we know about human beings, universal assent and support to anything is attainable only by universal and irresistible compulsion.
When people believe that they are engineering universal happiness and immortality (even or especially if this really were possible) then the end would justify any and every deployment of effective means.
Humans would be compelled to be whatever was required for Heaven, for their own good; and/ or humans would be replaced by something better-than (at any rate different-from) humans - who would go along with utopia.
Heaven on Earth must be utterly unfree - hence Hell.
Because Hell is not correctly defined as miserable, but as a state of permanent spiritual enslavement.
Hell is still Hell even when its denizens are compelled-irresistibly to
be happy - because then the denizens are no longer Men.
The condition of absolute unfreedom is the obliteration of the self, the person, the Man in essence.
Such a state may be chosen, Hell is apparently what some people - perhaps many people - want. But when Hell is imposed, as it would need to be to make 'Heaven on Earth', then Hell would become universal.
I'm not saying that this is possible, indeed I believe it to be impossible. The creator has not set-up creation to allow Hell to be imposed.
But I simply point-out that wanting Heaven on Earth is actually wanting universal Hell: it is to take sides with the agenda of the demons; with those who oppose God, the Good and Creation.
What about the Christian Heaven and its selectivity? Why can't Heaven be for everybody?
I hope that the above will help make clear why. My understanding is that selectivity is the only way that Heaven can be Heavenly, and at the same time free.
Selectivity is the only way that the denizens of Heaven can be real Men, with real selves, real agency; really participating in the work of divine creation (bringing their own distinctive, additional contribution to creation).
Death and resurrection is the means by which we can make a free and permanent choice for real-Heaven. That is why Heaven cannot be attained in mortal life, in this world.
Also; if Heaven is to be Heavenly, it must be freely chosen. If it is not freely chosen it is Hell.
You may, of course (you are free to do so) prefer happiness to freedom; in that case you have made your choice - which, as such, is neutral. But when you desire to impose that choice universally, you have chosen evil.