Answer:
An expansion of the idea behind this sentence could be: if the responsibility for something needs to be accounted by everyone but not somebody in particular, or not by some defined group of people in particular, then the responsibility is so diluted that it becomes nobody´s responsibility, that is to say, nobody takes charge of said responsibility. This could be a case for an argument against communal child rearing where, if the responsibility of child rearing rests on an entire hypothetical community, and not on parents or blood relatives, then it could be argued that the responsibilities, and the consequences, of communal child rearing would be lost and in fact nobody would really take charge of child rearing.