I'm not defending the Cas fans or what they were chanting because there is clearly no place for that in a modern sport environment (or indeed any environment).
However, I fail to see how the club can prevent it happening. You can put up all the posters you like, play endless messages over the tannoy, write it in your programme but the bottom line is if some imbeciles decide to chant then there's nothing you can do to prevent it.
You can take action after or during the chanting against the offenders but you can not prevent it from happening in the first place, so to charge a club for failing to do so is nonsense. You may as well charge them with failing to prevent it raining. Both are impossible.
I certainly wouldn't have any particular argument with that, but if what you say is true, how can the club claim to have "a well established system for dealing with chanting"? They could, as a minimum, have told the stewards to take a more active stance, but I have to say there was no evidence of that on Sunday.