I'm responsible for helping to kill spam on Quora, so I'm happy to hear that you've had a good experience. In reality, we get a lot of spam, but we also allow a

I'm responsible for helping to kill spam on Quora, so I'm happy to hear that you've had a good experience. In reality, we get a lot of spam, but we also allow anyone to edit most content so this crowdsourcing approach helps a lot. I'm sure the same is true for Wikipedia/StackExchange. No matter how large your site, if you give people you trust the tools to stomp out spam/bad content, they will use it and you eventually "win."