First, a Chaotic Neutral character wouldn't give a flying fig about anyone's rights but his own.
Chaotic Good: Doen't want anyone telling him what to do, and doesn't want anyone bossing others around, either. He'll stand up for the little guy being bullied.
Chaotic Neutral: Doesn't want anyone telling him what to do, period. Everyone else can go jump in a lake.
Chaotic Evil. Doesn't want anyone telling him what to do, and very likely to gut you if you try. Everyone else can go jump in a lake, and hell that sounds like fun I'm gonna TOSS you in the lake myself.
Second, the Terrasque isn't a monster, isn;t an animal; it is a force of nature. Comparing it to a hurricane is the correct way to view it. How many innocent lives would be lost by keeping it alive? The only possible excuse for allowing it to live would be if you could imprison it, or if it was a natural predator that, using an earlier example, kept the red dragon population down.
Anything else is irrisponsible. But, Cjaotic Neutral is irrisponsibility personified, so there you go. The two that keft were actually behaving as CN should, they just had the wrong reasons for it.