Obviously from their book burnings you can see that the Nazis weren't above destroying material they found ideologically objectionable, so I'm wondering why they encouraged viewers to see this art. Why go to all the trouble of showing art which they considered contrary to their aims?
Because the exhibit was an act of propaganda with "pedagogical" intent. The goal was to convince people that there was a (Jewish and communist) conspiracy against the German people. Some works were later auctioned off and others destroyed.
Some sources:
Article from huffingtonpost.com
Article from LACMA, "degenerate art the fate of the avant garde in nazi germany
Victoria and Albert Museum entry and inventory of the exhibition
Stephanie Barron, Degenerate Art
Olaf Peters et al, Degenerate Art: The Attack on Modern Art in Nazi Germany, 1937