The risk argument has got to be the weakest pro-capitalist argument of all. Let's see:

1. Workers take risks too, as Wolff points out in this video.
2. There's no reason that taking a risk inherently deserves a reward. No one will reward you for eating asbestos.
3. Once you get rich enough nothing you do is risky anymore. Elon Musk has lost more money than I could make in a thousand years.
4. The risk of a failed business is you have to get a job like everyone else. That they think this is so horrible says something about capitalism.
5. The reason it's risky to start a business is that you might not have as much demand as you imagined, you might lose in the competitive market, or you might get unlucky in a recession. In other words, this argument defends capitalism by pointing out that it's also a shitty system to most would-be capitalists.
6. Capitalists can make the decision to not shoulder the risk themselves at any time, but they never do. The whole "if workers are entitled to profits, are they also responsible for losses?" thing they like to say is just empty rhetoric, since they will never take yes for an answer anyway. If it's such a burden why don't they accept being relieved of it?

Did I miss anything?