No, I never answer my door with a handgun.
Because I have heavy plate glass sidelights, and if there is even the slightest suspicion on my part, I carry the converstion through those plate glass windows. I can either say "leave the box by the door," open my door to friends, family, or neighbors, or tell whoever is offering to clean my gutters that he has 5 seconds before I get my gun.
I know, he may have a shotgun and toast me as I stand there. What are the chances that a person will come to my door and just shoot me through the glass? That's an acceptable level of risk.
If that person tries to force entry or displays a weapon, I have a rifle in a closet about 10 feet away. I have seen quite enough premeditation to legally justify killing this guy if he comes into my home. He approached, knocked on my door, and after being given instructions that did NOT include "hey, come on in," he forced entry.
No, I won't be calling 911. The nearest phone is in another room far away, and inaccessible from that closet. No, I will not retreat, there is nowhere to go. once the perp comes through the door it is stand and deliver time. No other options that don't include being left totally at the mercy of someone who just illegally entered my home.