I have a family member who is quite into "ancient aliens" and who has read all of von Danikens books. The main thing I realized from arguing about it with them was that rigor and science did not really matter and would not convince them of anything. It's an emotional and spiritual belief for them - a way for them to rationalize how humans went from mud to computers. They don't believe in human creativity being powerful enough to lead to modern society and think an external force was required. Ancient aliens is a convenient and fun theory for how it could have happened.