Some BDSM activities may be regarded by vanilla people as being so peculiar as to be insane. Many countries even have laws that make certain consensual, safe activities between adults illegal on the grounds that anyone indulging in such activities is not sane.
Just as climbing up dangerous rocks in sub-zero temperatures with low oxygen can be hazardous yet is not a sign of insanity, so involvement in the relationships and activities discussed in this encyclopaedia can be hazardous yet is not a sign of insanity. What might be insane is to climb Everest without proper preparation and thoughtful care. Similarly, what might be insane is to undertake sadomasochistic practices, or enter a controlled relationship, without proper preparation and thoughtful care.
Playing sanely does not mean giving up the wild, abnormal or extreme. It means having due regard to the possibility of emotional harm and considering safety aspects before undertaking anything that has risks of physical harm.