The criticism's in this post really make very little sense. What does that mean that "private keys only have value when you hold them." Private keys are worthless, they only give you access to the wallets that they unlock.
Also, no, you are not guaranteed to stay at 51% forever. Vitalik has explicitly said that if a 51% attack happens, the community is expected to fork, and all of your funds will be isolated and slashed in the fork. If you want to attack again, you then need to collect another 51% of funds. This gets exponentially more difficult.
Also, no, you are not guaranteed to stay at 51% forever. Vitalik has explicitly said that if a 51% attack happens, the community is expected to fork, and all of your funds will be isolated and slashed in the fork. If you want to attack again, you then need to collect another 51% of funds. This gets exponentially more difficult.