British Columbia

You're taking a reasonable position and pushing beyond it's reasonable limits.

that is what things like the SPCA and law enforcement are for.

SPCA is a non-profit society. I don't think they have the resources to hunt down puppy mills actively trying to subvert prohibition. RCMP is a national police force. I'm fairly certain puppy mills would fall near the bottom of their priorities list.

Prohibition never works as a substitute for regulation. Look at alcohol, drugs, and prostitution. Not only does prohibition utterly fail at eliminating these practices, it demonstrably exposes people to exploitation and harm.

Prohibiting animal breeding would just mean that the people who chose to do it would have no incentive to ensure their animals aren't subjected to cruelty or harm.