Defining extremists to be "the people with unpopular positions" is defining extremists to be "those with positions most dislike." AfD are extreme because of what their positions are, separate from who does and does not support them.
Then show us their extreme positions! Their official party program is actually quite tame.
I never heard about their women-workspace-denial.
And being against marriage of homosexuals was the majority opinion from the beginning of time until around 10 years ago so you can hardly count that as extremist.