> We don't need an oracle to create this type of PM.
> The blockchain doesn't have to learn any meatspace information. It knows how much money was given to the crowdfund.
Yes, you do need meatspace information, to set the Schelling Indicator. Otherwise there's no way to control who gets the money.
> I think you can already do this type of crowdfunding with bitcoin.
Yes this is the Lighthouse project / Anyone-can-spend.
> Couldn't anyone make an altcoin to commit these same attacks that you describe for sidechains?
Yes, but the altcoin would not have sufficient mining power. This is discussed in the blog post "Oracles are the Real Smart Contracts".
> The blockchain doesn't have to learn any meatspace information. It knows how much money was given to the crowdfund.
Yes, you do need meatspace information, to set the Schelling Indicator. Otherwise there's no way to control who gets the money.
> I think you can already do this type of crowdfunding with bitcoin.
Yes this is the Lighthouse project / Anyone-can-spend.
> Couldn't anyone make an altcoin to commit these same attacks that you describe for sidechains?
Yes, but the altcoin would not have sufficient mining power. This is discussed in the blog post "Oracles are the Real Smart Contracts".