Overcoming reddit as a startup has a massive obstacle, moderation and removal of unwanted content. It's something that's not well automated, and thus requires an enormous amount of labor (ie capital) This is why those who have tried have turned into racist pornography filled shit holes. Want to start a billion dollar startup? Figure out how to automate this problem.
While some reddit alternatives might qualify as "racist", they've done a very good job at not being "porn filled shit holes", unlike reddit. In fact, most of the porn spam on these websites are images or videos hotlinked from... reddit.