Why are Trolls not blocked

Thats it. Why are the obvious repeat trolls not blocked from using this site by the mods?
I recently thought of quite the conspiracy theory.  The Troll is actually a ruse meant to frustrate users into opting for the Insider option to avoid the nonsense posts.  
In one way or another we are all trolls.  Who gets to decide when someone crosses the line?
OP Why are Trolls not blocked?
Because if they can be left alone to get to the other side of the road, maybe they will leave there mates and won't produce anymore trolls.
It's a future thinking thing.  
I too grow tired of the same trolls posting the same things over and over.  However,this is America,and as far as I know we aren't totally censored. Not yet at least. That means that even trolls get to spew their ignorance. 
  I just try to not view any threads started by the trolls. It's easy,because we all know who they are. Unfortunately,they don't always start the threads they pollute.