If you don't have capitalists who rents the building, buys the equipment, buys the raw materials, pays the wages and power bills before the first product is sold? How do you start a business without the Venture Capital?
Sure, you can bootstrap a business but that is a slow process and you probably will never achieve scale without Venture Captial so the business will probably fail leaving the workers and the founders unemployed and maybe in debt or just permanently small time.
If you don't provide a reward/incentive for the Venture Capitalist, why would they invest in your business?
If a corporation does not generate a profit for the shareholders why would anyone buy shares. If nobody will buy shares how can a Venture Capitalist profit from their investment (IPO) by going public. If you can't profit from your investment, why would you make that investment?
The alternative is non-profit businesses, charity cases. If all businesses are charity cases there would be a lot less business and almost no jobs.
To you title, no we don't need capitalists if we are willing for society to revert to a subsistence or spartan existence.
I will admit we have gone overboard on the consumer lifestyle and a massive reduction in consumption is needed but a balance is what we should be working toward not some sprint toward destitution.