I don't claim to fully understand the implications of ETFs getting into Bitcoin.
Neither do I, but...
At first thought it seems to be a positive thing (mass adoption, recognition, etc.). But, something makes me feel a little wary about such big players entering this space. All those massively powerful entities will have the power to greatly influence the market, and we must assume that their motives will not necessarily be pro-Bitcoin.
The problem is they will be able to do so without buying a single satoshi. That's why I advocate strict 'in kind' redemption (physical) and fastidious auditing. Which can only be done on the etf issuer reserves: it is impossible to do on the etf stock once it is out on the market. For a reminder, think of other stocks with short interest ABOVE the float.
It has happened, it happens everyday. GME is the latest famous example. And the asses of the shorters were saved by some opaque chain of factors - Robinhood, the clearinghouse, the antiquate short reporting system (they are going to update it to "within a working day" or so - why don't they use a friggin' blockchain or something?) - we will likely never know.
As a final note, I got my skin off GME while still decently in the green as soon as I understood that wielding my diamond hands would have given me no super tendies.