Using deadly force should always be the last resort. Just because something is within the bounds of legality, doesn't always make the right, prudent, ethical or moral thing to do.
I had a similar discussion with my brother 2 weeks ago when he told me he was going to purchase a shotgun for HD purposes. I told him to check the state laws regarding self-defense, but more importantly, just because someone breaks into your house does not automatically mean you have the right to kill that person. I told him that you have to use your best judgement. Killing someone is one thing but having to live with that split second decision, right or wrong, for the rest of your life is another.