Why do some guys get so offended about people neutering their pets?

This was initially going to be a question just for girls but I figured screw it, include men as well. Over the years I've heard multiple men get really offended by the notion of neutering their pets (usually a dog, I've noticed), and damn near throw a tantrum about it.
In this clip in particular, a vet says castration might be the advisable solution to solve a family's dog's overactiveness (even humping the children and their friends), yet the father says, and I quote;

"If your talking about chopping my dog's balls off, your talking about chopping my balls off. That's the way I feel about it."

Please, can people explain this line of reasoning? I just don't get it
Why do some guys get so offended about people neutering their pets?
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