It would be useful if each ePetition listed arguments for and against. These could be contributed by the general public, added under "Arguments For" and "Arguments Against".
There may also be comments classified under "Interesting Points" (please see De Bono's PMI system) and "Questions". The latter may have answers submitted by the general public.
It may require the webmaster to weed out duplicate points with the danger that this could introduce political bias. Therefore, maybe the best approach would be for the web master to bundle the duplicate points together, in chronological order, thereby making the system more manageable without deleting any opinions. They could be viewed by clicking on the original argument. Search software could make this task much easier and would reduce any "operator bias".