Well I'm not German so I can't really speak about what the AfD is about, and I'm sure there's a lot of actual Nazis voting for them. What is a topic however that is taboo because of association with Nazis is the influx of people with non-western ideals and values from Morocco and Turkey. Things like women rights, democratic ideals such as freedom of speech are under pressure as a significant portion of the population does not hold them. This problem is exacerbated when freedom of religion laws makes it so that subsequent generations are also educated with anti-western values. Mainstream political parties won't burn themselves on these issues, and the alternative political parties are often caught with Nazi's at their dinner tables.