Not only is Reddit's moderation system designed to prevent users from seeing content, the upvote system itself does the same. You'd expect a generic sub such as /r/politics to be somewhat neutral, meaning you'd find opinions from right wingers, left wingers, and centrists alike. Instead, you see nothing but anti-Trump and pro-Bernie posts because a larger part of the user base is left leaning. You could describe Reddit as a form of true democracy, in the sense that everyone gets one vote that determines the success of a post or comment. When dealing with a true democracy, you quickly run into tyranny of the majority, which is a big reason why right wing opinions are quickly suppressed on what's supposed to be a neutral sub.

This is why Reddit sucks as a political forum. Along with more open and honest moderation, you would likely have to do some serious changes to the upvote system, or do away with it all together.