The rest seem to be something moderation may help

Who will moderate? If it is a distributed system and moderation is also distributed bad actors can automate upvotes or whatever means we use for moderation to keep their bad content up.

Some of the ways abuse can happen

• Crawling false data / misinformation on a topic
• Putting info on search as part of a scam / spam campaign
• Putting false news about events that are happening, or have not happened at all
• Putting false information about a business competitor
• Putting fake reviews about a product

Just a few that I can think off… existing websites have the issues too, but what is different is how existing sites decide relevance and how often said algorithms weed out the bad content . In my opinion a distributed search engine will have a harder time at combating those, and other potentials for abuse, because there is less control about what is getting scanned there is an open policy of who can join the distributed scanning.