I wouldn't have a problem if they were upvoting themselves for good content. Manual curation has been pretty crappy and it's only fair that good content is rewarded.
Good content may be subjective but i think we can all agree when content is bad:
- thin content (single images or videos that aren't original)
- stolen images / videos
- copy pasta
Edit: The only way to stop this is when it becomes unprofitable for them. Some of the spammers have been upping their bids so this will probably reach its natural conclusion pretty soon.