A very small share of SpaceX stock is actually publicly traded for the first 90 days after IPO. It'll become much, much larger after half a year or so, and therefore so will the amount that index funds will put into the stock.
In this case, shouldn't the impact of a passive fund going into SpaceX be small to begin with in the first 90 days anyway, compared to the long-run amount of money going into these stocks? So even if the average investor takes a loss, it should be limited in impact compared to the counterfactual where the rule change never happened.
You are also ignoring the fact the in another incredibly rare and unusual move they are not allowing for any price discovery, and have fixed the price.
You know its bad when even Cramer...of all people...is panicking about what will happen to retail investors: https://youtu.be/8St2zNop9vs?t=125
Either way, knowing that there is a large buyer at the market price at known time intervals does still allow for some games being played in manipulating that price.
"Goldman Sachs expects SpaceX’s AI revenue to increase 100-fold by 2030" - https://www.ft.com/content/516cd0e5-a402-4b6c-8035-d688dc5f0...
Reminder what these guys are all about: https://youtu.be/jS9r1Dk-Zg8