It's the Cooperation, Stupid.

Capitalism is the utmost least worst economic system possible.

Capitalism is natural, and therefore the only sustainable economic system possible. Sustainable because it’s self-propelled. Self-propelled because of the laws of nature. The laws of nature meaning; capitalism is a direct output of the most universal and by far strongest instinct that all living things have in common, which is self-preservation, also known as survival instinct. The instinct of self-preservation is nature’s “invisible hand” that gives capitalism its self-propulsion. 

Capitalism is a paradox because; although it's the best system possible, because it’s the only sustainable system possible, because it’s driven by nature's most basic instinct of self-preservation... It's a paradox because the instinct of self-preservation also happens to be the very leading destroyer of capitalism (whenever not regulated carefully)."

But before getting into the paradoxical nature of it, here's a quick break-down of how capitalism is a direct output of the laws of nature in the first place. 

Self-preservation is life's strongest most universal instinct, Webster’s dictionary defines it as

1.  preservation of oneself from danger, injury, or death

2.  the urge to preserve oneself, regarded as an instinct

Keep in mind, preservation of oneself from danger or death isn’t limited to just the glaringly obvious goals of avoiding snake bites and shark attacks. Avoiding danger, injury, and death also includes (in fact mainly includes) acquiring food, water and shelter.

And it’s not enough to acquire these things on a moment to moment as-needed basis, so we do everything in our power to secure more than we need at the very moment. Beyond the mere as-you-go attainment of food, water, and shelter; our instinct of self-preservation deeply motivates us to keep our pantries and refrigerators stocked with a few-day supply, and to secure a permanent roof over our heads or at the least lock down a one-year rental agreement.

Here’s how Wikipedia describes self-preservation in a sub-section named ‘economic impacts’

Self-preservation urges animals to collect energy and resources required to prolong life as well as resources that increase chances of survival… The instinct that drives humans to gather resources now drives them to over-consumption or to patterns of collection and possession that essentially make hoarding resources the priority

And now let’s introduce an economics term whose definition should be considered synonymous with nature’s law of self-preservation aka survival instinct, which is profit motive. 

Profit motive is defined by the Oxford Dictionary of Economics as 

The desire for gain as a motive in economic activity

Considering that all survival activities are in fact economic activities in that both are life and death ventures involving dire competition, gains, and losses; what evolutionary biologists call self-preservation, economists call profit motive. It's more than an analogy, self-preservation equals profit motive. Capitalism is natural. 

But here’s how we misuse Capitalism…  

Abundance begets greater hunger for more abundance. Evolutionarily speaking, wanting more is the "invisible hand" that compels all survival-related actions of any species. But we as a species are so far ahead of all other species that we can and should better regulate the fruits of our collective outsize abundance.

Unregulated levels of abundance-accrual removes the necessary Competition-half of survival from the equation (for the very few winners) - thereby also destroying the lesser-discussed better half of our survival instinct, the Cooperation-half.