Just not having moderators - the end. The site has a voting mechanism that will take care of most spammers and other vermin
Not an option... it will just get filled with illegal things faster than people can vote (or bots will make voting pointless), and then people will leave.
bots voting is orthogonal to moderating. And illegal content: Maybe, but it'll get downvoted=hidden, so not a problem. "Moderation" is inversely proportional to quality in literally every online community in existence.
I don't think you can know that it won't be a problem, and I would argue it's already a problem in some places. Not all sites even hide downvoted content... and disagreements on subjective things will still mean even heavy moderation can't save some groups from being unwelcoming to a lot of people.