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.
The main idea relates to the comprehension of nonfiction text. We use the term main idea when referring to finding the big picture in nonfiction text. The main idea is the topic of the text and what is important about that topic. Details are used to support and give information about the main idea.
You need to identify appropriate rhetorical patterns for the topic and the task, and identify the components of an effective thesis statement. Hope this helped! :)
