Well this could water down to "ninjas are tools", which was examined in the Zabuza arc (credit to XanBCoo for the reminder). Even though they have their original spirits, they are still the attack dogs for whoever controls them.

It's like in Bleach, Byakuya's single-minded following of the rules of Sereitei and the judgment of the office of 46, even if it means his little sister dies.