How are you not trusting witnesses?
A relay is just another word for your server/hosting. When you login to a front end you will see all relays available and you can add it to your profile, and run with mutlples or spin up your own
Here's instructions on how to create a nostr relay
OK, but then Nostr is much more for IT-savvy persons only than Hive is.
Blockchains operate a consensus algorithm that is almost trustless. It is possible for anyone to validate the actions of witnesses themselves and even if that is not done, we can see that the system inherently incentivises and pressures the consensus witnesses to not introduce foul play. The only real way that the witnesses could cause problems for free speech that was undetected would be if they all colluded, no-one checked the situation and the people who were censored or cheated never spoke out. That situation has never occurred, to my knowledge. If witnesses collude and the community finds out, there will likely be a fork if the witnesses can't be removed - which is what took place when Hive was created from Steem.
At what cost? Forking reduces the security since its subsidised by the tokenomics that is the incentive to hold the data for others. Also if you fork why waste resources holding data you don't care about and thus prune the blockchain you fork
As the chain gets bigger it reduces the amount of people with the resources to do manage and you always have to trust a set of witnesses, moving the trust assumptions to a different party at great cost doesn't remove trust
In a situation where a chain has been corrupted by nefarious witnesses, the choice to not fork is the one that reduces security. I'm not sure why security would be reduced due to financial incentive in the way you are stating.
Whoever runs the fork can do so in whatever way they prefer. If the users don't like the way the fork is setup they can fork their own version.
If the processing requirements exceed the level of hardware that can be procured by the amount of rewards paid to the witnesses, then mitigation can be put in place that involves sharding, pooling or other strategies. However, we have never reached a point where this has happened.
I have already addressed this in previous comments.