I would be lying to myself if I would say that I'm not excited that BlackRock wants to be involved in Bitcoin and use it as an investment vehicle. BUT at the same time, we truly can't deny the FACT that custodial entities, if large enough, could be very dangerous for the future of the network.
ETFs are a slightly different concept to conventional custodians, though. They are effectively issuing shares based on the assets that they hold, rather than accepting deposits of the asset in question from their clients. And because they don't take deposits, it's unlikely they could engage in anything resembling fractional reserve, so that's not really a concern like it is with Bitcoin exchanges and webwallets.
Perhaps they are, but we are talking about BlackRock, one of the worldwide largest asset managers. It has ownership rights to most U.S. banks, own shares in most of U.S. pharma, they adminster 10% of all major stocks worldwide, they own shares in most of mass media companies in the U.S., and it is also the biggest asset manager that owns shares in major tech companies.
The total assets it manages is probably half of the United States GDP.
Plus it is now a major share-holder in 4 out of 5 largest Bitcoin mining companies,
https://finbold.com/blackrock-is-a-major-shareholder-in-4-of-the-5-largest-bitcoin-miners/I'm excited for Bitcoin-the-investment, but concerned for Bitcoin-the-network.