From very early in my online experience, I've found the two best ways to learn things are to answer questions, and to ask them. In that order.
By asking a question, you hear from others. By answering questions you're submitting a testable hypothesis and baseline which others can respond to, and which ultimately can only be improved upon. If I'm right, then others may either respond with less-correct solutions or misinterpretations of my comments. If I'm wrong (or not as correct as I might be), others can improve on my response.
And that's highly useful.
By restricting the availability of the responses to Quora questions, you're hurting that dynamic. And there are plenty of places (reddit, StackExchange, Wikipedia, HN, MediaFilter) in which those questions can be asked, answered, and extended.
I'll draw particular attention to MF: it's a pay-to-play system for responders. If you want an account, you've got to pay a $5 fee. Which is among the reasons I don't participate (at least not under this identity -- I've generally tried to maintain an isolation of this from my real-life ID), though if I found the site sufficiently useful I wouldn't object in principle. However I don't need to pay that fee to view the responses, and I'm more than free to refer to MF posts and extend answers on other sites.
Quora does not (readily) allow for this.
Add that they gratuitously block The Internet Archive and I'm done with them entirely.
I'm not going to play that game. I don't care enough. They've made it hard enough for me to see if I like their content that I'm not going to try. They lost their chance at me being a user by treating me like garbage.
I shouldn't have to 'impress the bouncer' to get in to read content they want me to see.
