Impact from moderation always goes both ways. The more you insert yourself, the higher the chances that your own stupidity warps the entire communication channel for the worse leading to shrinkage and echo chambers. And people dont vanish, chances are they are already attempting the next tower in babel a few ips over and get up to who knows what.
The merits of proof of work should be discussed for the specific scenario. If it allows for reputationless discussions and throwaway accounts, how high is the cost really? In comparison to banevasion problems, moderation overhead and the resulting attack surface requiring more resources while deteriorating the channel? Otherwise impact less emergency breaks for idiots might be reasonable solution. Its not much different from timed bans.
The merits of proof of work should be discussed for the specific scenario. If it allows for reputationless discussions and throwaway accounts, how high is the cost really? In comparison to banevasion problems, moderation overhead and the resulting attack surface requiring more resources while deteriorating the channel? Otherwise impact less emergency breaks for idiots might be reasonable solution. Its not much different from timed bans.