The followers of Chaos are often not particularly chaotic that's true. They often start pretty chaotic though. Chaos cults come in a huge variety of forms, everything from death cults to student groups, with an equally huge variety in mandate. The only thing they all share is that they are revolutionary, they are opposed to and opposed by the current order of their environment. Cults start off random and eventually mature into something more structured (or die off).
But there is a difference between Chaos and it's followers. Chaos isn't the Traitor Legions or the Lost and the Damned, it isn't even really the daemons. Chaos is the corrupting touch of the Gods, and while the end goal is always the same there are many paths that lead to that spot and many different starting points. People fall to Khrone through love of violence or through anger, a desire for revenge or power and through a miriad of other ways. Maybe they were a soldier who got a bit too caught up in the thrill of combat; maybe they were a policemen who got a bit too pissed with the scum he had to deal with daily; maybe they were just an office worker fed up with constantly being picked on by their boss. There's no real pattern there, no way of predicting who will be exposed or whether they'll turn.
That's what truly makes Chaos chaotic, anyone at anytime is susceptible. Anyone, anywhere can turn. There are no front lines in the battle against Chaos, no armies drawn up to fight, no tactics, no safe ground and no final victories.
"Look into my eyes, and see your death."
"Let them hate, so long as they fear."