In the latter case, the (theoretical) belief was that by improving the means of production and heightening the state of every individual's consciousness sufficiently, it will be possible to produce enough, and distribute fairly, whatever is needed to fulfill any individual's conceivable needs. My impression is that, unless we assume and infinite time scale combined with the evolution of human nature in the required direction, this is not attainable even if we further assume that the production of required goods and services will be possible. The evidence of human nature through the recorded history seem to show that there is (at least) one constant that can easily scupper any such brilliant plan: the propensity of humans to look at others and almost automatically wish for at least as much (most often decidedly more) than those others have, irrespective of a possible fact that both have more than they really need already. Since it is not possible for production to expand infinitely (see: basic laws of physics), given human propensity to envy and competitiveness, it will not be possible to have a society where each and every individual is fully content.
You now may object that I am unfairly invoking the infinities, and everyone knows infinities are impossible to reach (I love that ancient Greek definition of infinity: as far as you can throw your spear, and then a bit further). But look at it in this way: imagine everyone had all the transportable possessions one thinks one needs. Even if that were the case, people still need to live somewhere. It is also undeniable that people tend to be quite partial about exactly where they live. Another undeniable fact is that more than one person cannot share the same dwelling unless they are in a mutually agreed, and agreeable, relationship. You may argue further that it may be possible to create two (or more, indeed many) dwellings that are absolutely identical in appearance, content, and all the rest of the things people may care about. And you'll be right - but only partly. As much as such dwellings are identical, they can never, ever, be in exactly the same place (yet again, see: basic laws of physics). As close to each other they may be (e.g. on the same floor, on adjacent floors, on adjacent plots of land) it is guaranteed to happen that someone, somewhere, at some point in time will wish for the one he does not occupy, and the owner/occupier of it is unwilling to swap. We could now have a long discussion (think: until the cows come home) that careful planning, provided infinite or close to infinite resources, may be able to resolve all such situations to everybody's satisfaction, but I'll submit that this is, for all intents and purposes, an unattainable ideal. I bet that almost all of the population of the universe will in the end be involved in fine tuning such disputes (and not just about the dwellings, either).
So, it seems that the only possibility of realising the dream of absolute equality is engineering human minds, either through long and painful evolution, or by a directed effort "from above". But I have an objection to that, too. Not only is this likely to prove as long a process (think: infinitely long) as the pursuit of infinite resources mentioned earlier, but I think that in that direction lies the downfall of Man (and Woman, of course, I am being poetic, not chauvinistic). Why? The answer to that should be simple, really. The only thing that is certain to have always driven the advance of Man (and Woman) is the desire to have more. But how do you know you need more? Simple. Because you see someone who has the same (or is in danger of obtaining it) and you rush to achieve more lest they end up with more sex. Yes. Sex. Because sex means babies, and babies mean your genes live on. And once you have your babies, they need as good support as you can give them so they have a fighting chance of having a lot of sex, i.e. a lot of babies carrying your (and others', but you don't really care about those) genes. If there wasn't for this "arms race" human race would have stagnated. You may now think that stagnation is perfectly fine if you stop at a sufficiently nice and cozy point. But you think too small! The next species (maybe your own pet dog!) who continues to race onwards will eventually overtake you. It may take a good few millions of years, but it will happen. Oh, you can try and kill off all the other species, but for one you're unlikely to get them all, and two, if you do, you may as well continue applying the same reasoning to other fellow humans. But that's one wholly different story, and argument (and we may be some way down that particular road already), which I'll (maybe) leave for another post.
By now you may well be thinking that I think that human race is doomed to an eternity of misery at best, or self-destruction at worst. And you couldn't be more wrong. There is in fact a rather simple and neat solution to this apparent conundrum. It does require a small change in people's attitudes, but one that I think is entirely feasible. Once you realise that what looks like a final goal - getting the best of everything - is in fact unattainable as the arms race is literally unstoppable and never ending, you need only change your aim and start seeing the journey itself as something to cherish, alongside all the stops on the way where you enjoy the fruits of little victories. And if you look at it in a certain (correct!) way your life is full of lots of little victories. And little setbacks, too, but unless you're really, really unlucky they will be in the minority.
Finally, because right now, too many people seem to experience too many setbacks, and major ones at that, which are not of their own doing, we should also concentrate on moving the world towards the one where everyone is at least guaranteed the same starting position in life, and where there will be no unfair spanners thrown into some people's works. If we can do that, and it seems that humanity as it is now does have most of the resources to make it happen, then we can say we have already gone a long way towards the goal of everyone being as happy as can be reasonably expected. And if they are not, at least there will be a clear course for them to tackle and maybe get there, one down which the journey is at least as pleasurable as the prize that glitters at the end of it.
See? I broke my promise! I started off thinking I don't have much in the way of answer, and ended with at least half of one. I started thinking I cannot have my cake and eat it, and finished with half a recipe and a very nice aftertaste of the ingredients I tried and either rejected or chucked in anyway. While I cannot guarantee that I now have my glittering prize, I can certainly tell you that I enjoyed this particular journey. It has made me happy, and wasn't that the point?