"Just" is doing a lot of work here.
Many people have appreciated gains locked into their indexing products such that changing is very expensive.
The biggest issue is not SpaceX/Elon per se, but indexes bending over backwards for him and changing their indexing rules to fleece index investors.
Most IPOs perform badly, to the point where the SP500 excludes all of them for a year, and I think that is actually appropriate for an indexing product. Though they're looking to change that and their float weighting for Elon.
Though after doing some digging I am not personally meaningfully impacted since Vanguard uses CRSP, which is float weighted, so only 0.1% of that is going to be SpaceX and I can live with that.
I short the stock on the actual financials if I was exposed to it (and it was actually possible), but it's a small float and there are apparently tonnes of Elon fanboys propping up Tesla beyond belief already so I expect this to be one of the hardest to predict stocks/IPOs.
I agree that the rule changes are bad and ill intentioned, but I am not sure what I can do about it. And, even if it was zero cost for me to move to an ETF without SpaceX, I would not do it. The market does what the market does, that is what I signed up for, it is a lot smarter than I am. It is not worth changing that for an insult to what will be a few percent of my portfolio. Even if SpaceX drops to 1/2 of its IPO, it will be like having a typical down day, and it will recover. I do want a piece of SpaceX, I just wish it would be at a better price.
As far as the appreciated gains go, I agree with you. However, there is a strong correlation between someones wealth and how much they have in taxable. For most people, especially those that are not wealthy, their equity investments are heavily weighted to retirement accounts,so I look at this as more a rich persons proble.