What reasons does Carlson give for justifying the shooting of Candy’s dog?

Carlson begins complaining again about the smell of Candy's old dog. He also notes that the animal is old and crippled. He goads Candy to shoot the dog, which Candy refuses to do. Carlson then offers to shoot the dog himself. After Slim speaks up in favor of shooting the dog, Candy reluctantly allows Carlson to take the dog outside with his Luger and a shovel.