John Lennon’s “Imagine” was a depiction of what he considered to be a utopia:
But if analyzed closely it sounds quite dystopian in a way.
This means that there being no afterlife and that people will die in one life on this Earth. It will mean for many people that life is pointless and encourage them to engage in hedonism or suicide.
This would mean furthermore that humans would have no great purpose for the future either of a religious or secular nature encouraging trends I mentioned above.
Further emphasizes that in this society life would be meaningless. If you don’t have something you’re willing to be a martyr for than you lose a certain drive in life, a certain will.
Considering this society would be communal at best, even the enterprising drive will be suppressed.
In conclusion life in such a society will be pretty much pointless without any greater purpose for humans to live for. Most likely humans will largely abandon themselves to hedonism or kill themselves. It would also be highly vulnerable to extraterrestrial invasion since presumably in this society military would be abolished.