Sad, especially when ithere's some little kid there with them.
That's why I am not an "Angry Apostate" on the doorstep. What I say to the adults is normally a message for the kids to hear.
"yeah, I was brought up as a Jehovah's Witness and used to be dragged round on the ministry on Saturday morning instead of doing something fun on a beautiful day like this. I did a lot of research when I got old enough, discovered it wasn't the truth and that we were just doing the bidding of a bunch of old guys we'd never meet so I left and life's been so much better since. Now I get to enjoy beautiful days like this doing things with my family instead. Life is just so much better when you leave the fairy stories behind".
Anything to promote the idea that you can question things and you can leave and be happy.
If they don't have kids then I like to get them to read a few scriptures to get them confused with their own doctrines or talk about the ridiculousness of the Adam and Eve story until they take the cop-out-route of "it was just a story" and then ask "so if you believe in Jesus, what did he die for?".
It's fun to see them utterly confused. Who knows, it may make them question things. We all know that if someone asks the Elders for answers they will often be told to shut up and keep quiet. There's the answer they need to hear to know the truth.