This study was addressing comments rather than posts, and suggested that comments are adversely affected by downvotes. That said, I'd argue that its very easy to get a similar sort of posts based on upvotes alone compared to upvotes and downvotes. Reddit doesn't seem to demonstrate that downvotes work in general against specific types of content, but are in fact subreddit specific. As a result, the signal of total upvotes and the signal of upvotes + downvotes will be similar. However, this study demonstrated that this is not true for the majority of people. In the end, it is not what ought to be which determines the content, but what is.But without down-votes you end up with silly facebook and 9gag content.
If you stoically see downvotes it should not alter your mood. You are the master of your mood, not the random people that dislike your comment, or weather or politics.