POW is permissionless, in that you don't need anyone's permission to setup a mining rig and contribute significant work.
POS isn't permissionless -- you literally have to buy a stake from existing holders in order to participate.
POS isn't permissionless -- you literally have to buy a stake from existing holders in order to participate.
The probability that a raspi ever mines a block (like, if it were to start now, not if it was going since the network first started) is negligible.
Therefore, I consider the probability that a given raspi would contribute to the security of the network, or, I suppose equivalently, the degree to which it contributes, to be negligible.
Yes it is. You can manufacture your own mining rig, with no-one else's permission, without ever needing to so much as communicate with anyone who currently holds any bitcoin.
> To add insult to injury, most miners ignore the externalities of that electricity use.
Most cryptocurrency developers ignore the externalities of all the crime they're enabling, so it's not like the miners are any worse.