So if I got you right, you’re saying ETF holders like BlackRock will just jump in and tweak Bitcoin’s blockchain code — all for our ‘safety’?
They can always decide to fork BTC, anyone can do it - the only question is whether they would do far more harm than good for themselves and their clients. When the time comes for quantum-resistant BTC, it will be done by BTC developers and implemented with the support of the majority of the community.
Remember how that went when SegWit came in? Plenty of miners weren’t on board, we got the Bitcoin Cash fork and a whole army of other forks. I counted 69 versions of Bitcoin back then. And BTC lost 50% in value. Good luck repeating that drama
All of these forks are mostly insignificant, and only one was a somewhat serious attack on Bitcoin, which of course failed despite the huge amount of money invested in it. The majority of the community followed the original BTC and even if a new fork were to happen initiated by some powerful companies like BlackRock, again only a part of people would decide to follow their chain - because any centralization is completely opposite to what makes Bitcoin so attractive to all investors.
Spot BTC ETFs have definitely changed the way people invest in BTC, so even though those of us who do it the other (correct) way may look at it with skepticism, it's simply something that had to happen and will play its part in the history of Bitcoin.