The cycle of social media I guess.
Consider that most "purges" happen to coincide with bad PR and you'll understand that's what their motive is.
One good solution to this problem is as following:
* In order to post content, accounts must be purchased based on a spot fee. For example, if suddenly 10 fold more people want to open accounts then spot price will rise to 60 dollars from a base price of 6 dollars.
* This can be done through BTC payments instead of dollars to protect identity of account owners a bit.
* Users should be able to hand-select moderators and if wanted, review their actions transparently. This will eliminate all unfair moderation and provide huge value to users. An user still can get banned by a moderator but only people who subscribe to that moderator will assume user is banned.
* As accounts are bought to post content, there won’t be any advertisement. There might be some subscription fee though.
* All this can be done in a decentralised framework to increase resilience.
And unless you put a similar fee to unlock voting, you don't prevent a whole class of issues with bots.
Random internet user would purchase an account if service provided value for them. For example, maybe they can create forums via this system for their gaming guild etc.
Yes, advertisers can purchase an account but there might be a popular moderator who bans these viral advertisements, based on popularity of ad-blocker I imagine such an moderator would get bunch of subscribers. Perhaps moderators can make some money through their subscribers as well, might be an interesting scheme.
Also spot price is pretty strong deterrent for advertisers especially if they keep getting banned through popular moderators.
I can see some users pay the fee so they can downvote opponents, but otherwise why would they? And of course they can still pay a higher fee to downvote multiple times, if they are angry enough, which is exactly what you wanted to prevent in the first place...