The problem of Reddit (and Raddle) they can't separate post written by users or just post a link. The downvote system is another problem.
Most posts on Reddit just a link to the mainstream media. They should set a "written by users(+ set as default) " button on every subreddit to separate 2 different kinds of posts, otherwise, everyone just reading what the mainstream media want them to read and lead to less communication to others. Maybe this is the original purpose of Reddit. (Although Raddle is not such "mainstream")
The downvote(and karma) system is a thing to threatening people: how dare are you not being mainstream? I know there are some assholes often getting downvotes, but this is very bad for self-expression of the minorities. And I am sure they can buying downvotes as buying "likes" on Facebook. So if you wealthy enough, and you hate a certain topic, you can buy tons of downvotes for it.
It's too easy and simple to see through what these websites are doing...Give space for anyone have enough money to control what sheeps thinking.