The issue of forum boards that have a voting system is that they promote a certain "hive mind" attitude.
The main problem is that it discourages many people to make threads that may go against the current mindset, because they fear they could be downvoted - so essentially it promotes one single line of thinking and silences the others.
It also makes it so that if a forum member dislikes another forum member, they can and will downvote anything they write. That's a sort of mild "bullism" as well. For example, every time I make a thread I get one (1) downvote immediately after.
Lastly, it often makes the main discussion threads to be about praise, while discussions and controversies are hidden under a wall of downvotes.
Now keep in mind I'm not talking about MY threads: when I'm aggressive, I expect my share of downvotes. I am talking of the boards as a whole.