Well, the Budesamt für Verfassungsschutz (office for the protection of the constitution -- not generally known for their left-leaning point of view) classified the AfD as proven right-extreme. On that ground outlawing that party has been considered; this hasn't been done yet, partly due to the popularity of the party in some regions -- there's the danger to further alienate the populace there, many of which are already disenchanted with the earlier established parties. Some consider it best to let them govern for a while and thereby demonstrating that they can't solve intractable problems either. Others fear that they will cause irreparable damage even in their first days in office, e.g. cancelling the contract for public broadcasting service.