It also happens to be the only thing that can possible be used to govern and upgrade a Bitcoin-like system. But it’s not Bitcoin, as a technical system, that relies on it but rather Bitcoin Community as a social entity that relies on it.
For Bitcoin, as a technical system, any change to the rules means death and replacement by another system. That the replacement system is called Bitcoin is a social convention, not a technical one.
The point here is that it’s much simpler to verify consensus when there are clear technical rules for how to do it. Moving from PoW to PoS replaces a very clear and easy to understand technical rule with a complex social construct that’s very difficult to understand all the subtleties of.
In other words, in a PoW system, it’s easy to understand what an attacker needs to do to attack. Therefore, everyone can effectively participate in the defense.
In a PoS system, very few people, if any, can completely understand what an attack can look like. The deceptive part is that while there are easy to see obvious attacks, which can thus be easily defended against, there will also be subtle attacks that might not even be perceived as attacks until after the damage has been done.
It’s bad enough to have to rely on social consensus for upgrades. Let’s not rely on it for the basic operation of the system too.
