Earlier quoted context omitted.
Mein Kampf was published 1924 and distributed broadly. There was not much hidden, the goal of making a big war in the east to conquer new land for the Aryans was there in big letters in the open. His views towards jews likewise. So they knew. Maybe largely did not wanted to know. And they did celebrate the victories of the german army as their own. They only stopped celebrating after the victories stopped happening a…
You had to take him seriously but not literally.
" Each animal mates only with one of its own species. The titmouse cohabits only with the titmouse, the finch with the finch, the stork with the stork, the field-mouse with the field-mouse, the house-mouse with the house-mouse, the wolf with the she-wolf, etc."
(from Mein Kampf, Chapter 11)
But if no one would have taken him serious, there would not have been a problem. But people did take him serious, they seriously believed he was some kind of messias send from god to save his troubled great country.