It is if your goal is to control (or at least influence) the Internet zeitgeist without appearing to...
That's a propaganda success, not a business success. Reddit has always lost money, and continues to lose money quarter after quarter.
My theory - Reddit is kept alive by YC and YC-affiliates to keep the "hype" engine around their investments alive. In other words "remember, this is from the smart people that invested in the Frontpage of the Internet™!"
Since when is being associated with Reddit a huge signal of success, esp. compared to other sucessful startups?
Keep in mind that Reddit was pretty much PG's idea, not the founders'.
It is not successful for the owners. It has been a very successful project for native advertisers of all stripes, and people that are insane politically (of all stripes).