Capitalism, as defined by Milton Friedman, refers to 'the organization of the bulk of economic activity through private enterprise operating in a free market...a system of economic freedom and a necessary condition for political freedom.' Friedman thus defends capitalism not for its own sake, nor even for its capacity to create wealth, but because of its association with individual, economic, and political freedom. The first thing to note about freedom is that it does not produce equality. So people wonder whether all this freedom is fair, and to the extent that it is unfair, whether it is immoral. Is it immoral to promote freedom if it ends up in a situation where some people have more stuff than others?
John Tomasi's work on The Moral Case for Economic Liberty sheds light on this question. The first issue to address is the popular association of capitalism with infuriating amounts of wealth, i.e. the idea that a capitalist is by definition a tone-deaf person who struts about dripping with diamonds, ignoring the poor, and saying annoying things like 'let them eat cake'. But in the sense defined by Friedman, the capitalist is any person engaged in any form of private enterprise: working hard on their own account to produce or earn the reward that they have chosen to pursue.
The idea of personal choice is therefore central to notions of freedom. And personal choice matters even if it produces a lesser amount of wealth than that produced by someone else's personal choices.
Problems begin to arise when people claim that owing to circumstances beyond their control, they are not able to make any meaningful personal choices. For instance, one cannot make a personal choice to dine at the Ritz if they don't have any money to pay the bill. A child cannot make a personal choice to excel at school if they have a chaotic home life and they're on the brink of starvation. So it looks as though personal choices are the luxury of those who already have significant material means and privileged, carefree, easy lifestyles.
For that reason a moral defence of capitalism only works if you believe that people always have a choice: they may not have a choice about their material conditions, but they have a choice regarding how to respond to those conditions. This is essentially what makes us human: our ability to choose how to respond in any situation.
Choosing to acquire things by forcing other people to provide them is not the best choice. Far better would be to choose to acquire things by one's own effort.
When you open your eyes and start to look around, you soon notice that very few successful people have a personal story about how easy life was for them growing up, how much their life spilled over with material advantages, and how they always had everything handed to them on a silver platter. Instead, a life of hardship usually lies not far beneath the current trappings of wealth: if not hardship in their own childhood, then in their parents' or grandparents' life story. Don't be fooled by the very few cases who can trace their family wealth back to the dawn of time because their bloodline runs back to Plutus himself. Such cases are not statistically significant. For the vast majority of human beings, the truth is that hardship is no reason not to make personal choices that ultimately lead to success. Hardship is therefore no excuse for doing nothing to improve one's own conditions, nor is it sufficient justification for forcing other people to share what they have earned.