Most kidnappings are intra-familial, at least in the US—mostly related to child custody disputes. Are you saying that the police shouldn't get involved in those cases, either?
Aren't most of these kidnappings also intrafamilial? Even if you throw out the "parent returns a kid a bit late from an activity" cases, I think there are many more parents trying to take kids to another state to keep them full time despite a custody agreement otherwise than there are strangers just nabbing kids in parks or what have you.