1) Firearms are lethal.
2) Dogs (can be) lethal.
You don't hear about Chihuahua's attacking people because they just aren't very lethal. Despite what the Chihuahua might think!
Same holds for black guns vs. .22 single shot rifles.
People own firearms for protection. Also, for sport/fun.
Same applies to dogs.
Also keep in mind that:
Some firearms have a tendency to accidentally discharge. Despite manufacturers attempts to avoid these issues.
All firearms should be handled with proper gun safety protocols. Regardless of their safety record.
Some dogs have a tendency to be violent.
All dogs should be handled the same. Hey, dogs have bad days also!
One huge difference is (as someone stated before) dogs operate on their own. You can pull the bullets out of a firearm and store it. You can try storing (caging) a dog, but they can also work at getting out all day!
It's a difficult debate for sure.
People on both sides of the fence. The same holds true of firearm ownership.This is a great debate, because it sheds some light on how anti-gun rights people might view the 2nd amendment.