Perhaps that slogan could be taken as a summary of the feeling that lies behind the mainstream Leftist movements, and their strategic attempts to reshape human nature with propaganda/ education/ media censorship - and, increasingly, technology.
The 'insight' is that if everybody 'chose' to behave in such-a-way; then there would be no problem about people behaving in other ways. The difficulty is then 'merely' getting Everybody to behave such-a-way.
This is why totalitarian behavioural control at the core of the Leftist project - whether or the Marxist Old Left type or the Politically Correct New Left Type. And it is why Transhumanism - the technological re-shaping of human nature, replacing humans with something-else - is the implicit goal of all this-worldly, hedonic Leftism.
The Utopian hope is that once badthink has been eradicated - by total control of human perception and cognitions for, say, three or four generations; then people could again be freed, and left to their own devices. (e.g. The Marxist belief that the State will 'wither away' when it has done its job.)
The hope is that when the world has been utterly ridded of bad behaviours such as snobbery, sexism, racism - when such ideas have been totally-excluded from public discourse and private contemplation - then the world will have been emptied of evil. Emptied of all preventable suffering.
People will then, quite naturally and spontaneously, be Good - they will not know how to be other than Good...
(Behind this is the idea that people are born Good, are naturally Good, and would stay Good unless or until they are made bad. The job of the State is therefore to exclude all bad influences - and you can see this assumption at work ever-more thoroughly with every year.)
There a a number of unjustified assumptions and inferential flaws in this reasoning; but perhaps the most striking is the problem of who defines Good and evil?
If Good and evil are passively absorbed-from society - how could we ever know about them? And who (in advance of Utopia) stands-outside of the prevalent evil such that they can engineer a future society of Good?
Such questions becomes insistent (one would suppose...) if it is ever noticed that there is disagreement about what is Good and evil, or that Good and evil change through time.
Such noticing ought to lead to an examination of assumptions.
Yet it does not. The assumptions continue, unacknowledged, unexamined.
And that is the real 'mystery' of modernity. How does it explain its own morality? Whence cometh the knowledge of Good and evil required to engineer the Good society?
At least it is a mystery unless we suppose that there are indeed intelligent Beings that do stand-outside-of the social system that they have created and sustain; and manipulate it purposively, strategically...
Demons, in other words.