I think there are two ways you can kind of get going on the theme approach suggested above.
The first is to list all the specific examples you can think of - why do all the specific disagreements occur? Get a nice long list of all these concrete examples, then go through and see if you can group them. Do any of the examples kind of fall under the same category as other examples? Figure out what the common idea between them is, and you have your paragraph topic.
The second is to go through your list of themes in the text (if you don't have one, you should get one! there's no absolute list - it's just one that works for you, taken from class, Internet etc). For each theme, ask yourself whether you could argue it affects the ability of people to agree, or relates to the ability of people to agree. For example, prejudice is one commonly-listed theme. This affects the ability of people to agree. The meaning of justice is another theme. Once you have three themes you could link to agreement, you have your three paragraphs. Then find some examples/evidence for each.