No one is being suspended or banned for just speaking their mind as long as they're within the forum code of conduct. That can include reposting threads that have been deleted, though.
What might be happening fairly regularly is that threads are being deleted because they're on topics that exist in many other threads, and/or have been discussed a great deal.
We realize that many people want to have a thread that is their very own and provides their own voice to commentate on why they think something is a bad change, or what have you, but we do have to keep rest of the people reading the forums in mind and keep topics to at least some standard of variety. You can generally see in these threads a great deal of hostility as most forum goers are just simply fed up seeing these topics over and over, and while those fed up individuals can themselves cross the line and earn a vacation from the forums, we have to attempt to understand the cause of their frustration, and I don't believe it's wrong to remove those repeat threads to create a less hostile environment.
In any case, repeat topics is what I have found to be the reason for 90% of thread deletions that people perceive to be 'deleted for no reason'.
Neth made a pretty lengthy and good post on some basic information about how we expect these forums to work. I recommend giving it a read if you have not already:
http://us.battle.net/wow/en/forum/topic/2016792409#1
I am sorry but these forums often don't promote any form of discussion. Topics seem to be deleted if they might have a negative effect on blizzard. Examples:
Comparing different MMOs to each other, Quarterly earnings of the company, constructive criticism of the expansion or patches, problems with classes balance or anything else that would remotely paint blizzard in a negative light.
Yes some of those posts break the rules or are just plain troll post however many are not.
These forums also seem to keep the silly threads on the front page for days while anything worthwhile gets pushed to page 10.
If you are worried about repeat threads then lock them but redirect those viewing it to the thread you wish to keep open.
On my side of the fence it looks like you are just randomly deleting threads
