1. Predictable BTC loss is destabilizing. Every transaction includes risk of loss, meaning a greater portion of supply that is immobile will grow. No, that's not solved with divisibility. The world cannot have confidence trading it's wealth in 1 million BTC with 20 million sitting on chain immobile. If another million can suddenly wake up because an unknown pool has been hoarding them, it wrecks the market.
This might be an issue when more and more people decide to HODL and the liquidity dries up. But the market should correct itself, prices will go up quickly until people start to consider selling again. We will just start trading in always smaller quantities, until prices drop when the majority of HODL investors start selling. This is not something that is only happening in the crypto world. The stock market faces the same risk and is doing fine for the last 100 years. I don't this is going to be a big issue in the crypto world. A company can just issue new shares overnight and dilute the existing shareholders putting pressure on the price. Or some of the wealth, or large college, or retirement funds that hold large portions of companies could rebalance their portfolios, sending prices down. There are a lot of stocks that are not actively being traded and the market is still doing fine. As long as everybody knows about the issue and can adjust his expectations there is no problem.
Despite the reasons so far mentioned, the long standing history of its existence will speak for it and all of us who use it will not be able to HoDL at once so as it becomes scare or unavailable.
The halving should be one corrective measure to instigate the market seasons that would cause buying and selling in large quantity, hence why it would keep existing even if the ETF is failed to be implemented.