If you read my footnote, I actually think something LS-LMSR-based would work better. I avoided bid/ask-based markets just because I am trying to simplify the strategy space and keep it to just “upvote or downvote or do nothing”, though bid/ask-based markets could theoretically work too.
so a simple programmatic way to win votes would be to always vote yes as fast as possible. What would happen in situations where there are 0 “no” votes?
If there are 0 no votes, then yes voters do not earn or lose any money. Earning or losing money only happens if there is a nonzero quantity of voters on both sides. Remember that these markets are NOT pre-funded.
In the rare-but-obvious-spam scenario, why would anyone vote the content up?
To increase the length of time that innocent victims see the message. Unfortunately it’s definitely not a Nash equilibrium for there to be a literally zero rate of successful manipulation precisely because in that case there would be no incentive to downvote, but if manipulation can only be slightly successful then every manipulator is effectively contributing to the bounty pot that encourages everyone else to downvote and vote against them and other manipulators.
Also - couldn’t a spammer post spam and immediately vote it down at very limited risk - and then have upsides both from the spam being accepted and being rejected?
The spammer only has upside from downvoting the spam if others upvote it; if no one upvotes then downvotes are not rewarded. This is also why we can’t pre-fund on-chain market makers.