You are obviously correct that the more value this tool has, the more work bad actors will do to take advantage of that, reducing the quality of the result. However, I do think Reddit is more resistant to it than some other platforms due to the large amount of distributed work done by the participants. Assuming that a given subreddit is moderated in such a way that the vast majority of participants are individuals interested in high quality products then the Reddit voting system does help to keep other stuff out.