Capitalists will resort to a lot of self-serving rationalisations and justifications for their status and for capitalism itself.
I was going to avoid simplifications, but here it is.
Capitalism is a system in which the very means to life and material well-being is controlled and owned by small class of owners. Those who aren’t these owners—they have to work for a wage (or face the social stigma of receiving state benefits and/or destitution).
Here’s the trick: The sum of all wages earned by workers is never enough to buy back all that workers produce. Where does this “surplus” go? I once asked a Libertarian™ this question, and she literally couldn’t comprehend it no matter how I rephrased it or explained it. Go figure.
And how on Earth is this relationship between owners and wage labourers a “voluntary” one when there are practically no alternative options available, and not working means social stigma or destitution? And no—some individual rags to riches stories aren’t relevant. The class division is systemic: We can’t all be capitalists.
But there’s a more important point. Why should the means to produce be the preserve of a relatively small class of individuals at all? There’s no real justification for that—it’s a vestige of history (a bloody, murderous and coercive history that required massive amounts of state violence, and forced transfer of wealth and resources).
If we were to start completely from scratch, if we simply landed on Earth as it is with all the systems of production, distribution, and resource extraction in place as they are now—we wouldn’t apportion 90% of it all to 1% of the population (Here’s a clue: such a skewed distribution would require massive amounts of force and coercion). That would seem insane, and grossly unfair. Yet, it is exactly what we have.
We mostly accept this form of economic organisation because we’re born into it, and don’t know any better. It feels natural. It feels like there’s no better way—and indeed, there is a whole industry that’s developed simply to reinforce, indoctrinate into, and justify capitalism.