Why would anyone want to cure such a gift?

To quote Syndrome, "when everyone is 'super', no-one will be"?

I think that Callie is a werewolf. That would explain why she was against killing the lycanthropes at the beginning of the story. Since she's suffering a werewolf condition too, she doesn't want to kill people like her. She hopes that during the werewolves would lead to a cure to her condition.
This also explains why she was enraged back when Endy accidentally turned her into a dog. It probably brought back bad memories of her unwilling transformation. This is why she drops Eddy's hot food on him despite Endy not turning her on purpose and trying to fix the mess.
Frankly, I never supported Callie's idea of protecting the werewolves. In real life, it would result in unnecessary death because containing them is hard. Even the comics showed that getting a cure was hard, mainly from a rare blood donor from another dimension, which later turned ineffective.