@nprofile1q... The second sentence is misrepresenting the real threat.
The problem isn't that SpaceX could get billions of dollars from passive investors. The problem is that if it joins the index, due to the company's huge valuation, the index would have to be re-ballanced, meaning the percentage participation of other companies - reduced. Which would have meant huge amounts of selling of the stocks of those companies by passive funds that track the index. Which, on its turn would have screwed up the investors in these companies.
And, sadly, while SpaceX won't become part of S&P-500 or DJI soon, it can still become part of Nasdaq-100, Russel-2000, etc., which will have a similar effect. So, only one part of the problem was averted.