That's an important point. It's so hard to think of a better system, if you take the task seriously and actually think through all the consequences of each option.
As a result, as usual, the loud people that ignore all the details end up capturing everyone's imagination with a good story, and we stumble upon yet another century of nightmares.
Do you truly have a answer for a social architecture that is substantially better than a capitalist social democracy, flawed and compromised as it is? Because I really don't if I'm being honest with myself, and I am yet to hear one.
I think the problem I find with arguments that Capitalism is the best/least bad system tend to be that they start from a false premise, in my opinion. I have a friend who makes the joke all the time that any system of government works if people were just nice to each other, but he has a point. I often hear that "oh, communism doesn't work because humans are inherently selfish." That's true, if you believe that humans are inherently selfish, but my counter-point to that is asking how much of it is innate vs. how much of it is trained by our culture and reflects back in those communist attempts because the sudden change in social architecture didn't give enough time to 'train it out of' the culture.
Back to the thing my friend says - if you believe that communism doesn't work because humans are inherently selfish/greedy/etc, I'd say to you also that capitalism is currently not working _because humans are being selfish and greedy_ in a system _that explicitly rewards that_. Which, maybe is worse. Not as in the outcomes are worse immediately than Soviet Russia etc. but for the long-term trajectory of human society.
I don't pretend I have an answer for how we can get from point A (capitalist system) to point B (future space communism) in a way that slowly shifts human thinking towards mutual aid and collective action, but I think it's short-sighted to assume that the way humans act in a system that rewards greed/selfishness is innate.
That's one way to put it. Another perspective (mine) is that capitalism enables anyone to try and make things better, and if you make things better for the right user, they will reward you.
Fun techcentric utopian speculation about this: Cory Doctorow's "Walkaway" and Ruthanna Emry's "A Half-Built Garden."
Essentially, can we leverage our current post-scarcity society to expropriate everything people need in a sustainable way that cuts capitalism and the State out of the loop? For example, why would people buy food if they can get it for free from farming syndicates or similar? (see: Global Village Construction Kit, Food Not Bombs, Food Not Lawns) Why would people buy medicine if they can print it for free from pirated recipes? (see: Four Thieves Vinegar Collective)
I see the Right to Repair and FOSS movements as a foundation to build upon for this. Anarchism (or at least, anti-capitalism) exists right under everyone's noses, in all the FOSS software installed on their computers. Existent example of people laboring without profit motive and contributing to the commons.
My personal life goal is to figure out how to capture that same energy to tackle the bottom layers of Maslow's hierarchy.
I'm not entirely cynical, people generally are very open to be generous with one another and collaborate for a common good, but up to a point.
Currently people spend the majority of their hours doing relatively hard work for the collective's benefit (kinda). Exactly because capitalism makes selfishness into selflessness (very kinda). Also people are relatively civilized to one another thanks to the considerable latent force of the state's monopoly on violence.
People will be nice to each other when it doesn't cost them much and/or when the opposite costs them dearly. But will they work as hard as now for each other just to be nice? Will they not harm each other when there are no significant consequences and something to gain?
A fair free market is far from a natural phenomenon, it needs to be protected and maintained by some external force. If you let things unfold naturally, what you get is kings, and many layers of dominating hierarchy underneath, exploiting the masses, which exactly what we had the whole time.
I suppose that the post-scarcity idea is that people neither need to work hard, nor have significant reasons to harm, if they have everything they want. Sure, let's talk if we ever get there, but until then we have other problems to deal with.
PS: Don't forget that people are able to do FOSS because they have well paid jobs that don't completely drain them of their energy. For others, getting the reputation and/or experience for a better job is the incentive. There's a very different social infrastructure making that work, FOSS doesn't sustain itself, not even close. But yes, it does prove that when people's needs are covered, some of them will do great things for everyone without much incentive, but usually not enough to cover everyone's wants.
What I am weary of is that such experimentation, and the energy it generates, will eventually be overtaken by the next iteration of people who want to stop nibbling at the margins and break a few eggs already, some sort of anarchist revolutionary vanguard. Much like with communism, skilful opportunists with a thirst for power will be all too happy to take over this energy and direct it toward building the next totalitarian regime, one which will of course claim to be rendering the State obsolete, but will be about as anarchist as North Korea is a people's democratic republic.