Anyone could mine and / or create accounts for relatively cheap. Even at the current difficulty levels now, you can mine 10 names a day (if not more) for a month at only 60 USD. That's 300 names for 60 USD. Now, do that with 15 servers (less than a grand) and you have 4500 names.
Then, it's relatively simple to write scripts to upvote content and you have sybil. Once you have a limiting rate effect of SP, you invite this type of attack.
In addition, it adds additional strain on network.