The public markets definitely are for venture investing that was their origin and still is a main function today.
I guess it all depends on what you call venture investing. I don't think that Sergey and Brin could have IPOed 6 months after founding Google - the public would have found the idea of investing absurd. So instead they went to VCs who can actually realize value in a "idea" and are willing to invest at a reasonable valuation.
Raise enough VC money and you can advance the company forward enough so that the general public see value in your company (usually revenue). At that point you can IPO and actually get a decent valuation.
I guess it all depends on what you call venture investing. I don't think that Sergey and Brin could have IPOed 6 months after founding Google - the public would have found the idea of investing absurd. So instead they went to VCs who can actually realize value in a "idea" and are willing to invest at a reasonable valuation.
Raise enough VC money and you can advance the company forward enough so that the general public see value in your company (usually revenue). At that point you can IPO and actually get a decent valuation.