Sure it is...
If your dog attacks someone in your yard, you are liable. They can protect themselves from your dogs all they want and be within their rights to do so. And personally, I carry 90% of the time and I will shoot a dog that attacks me regardless of where I am.
As far as answering the door, I usually check to see who it is and if unknown, I begin by talking to them thru the door while determining whether to open the door with my hand on the j-frame.