Value of information about which political side is more marginally valuable makes unbiased discussion a cause that's potentially more valuable than advocacy for any of the political sides, and charities are similarly on the same scene. So the rule is not "focus on a single element out of each class of activities", the choice isn't limited to any given class of activities. Applied to politics, the rule can be stated only as, "If advocacy of political positions is the most marginally valuable thing you can do, focus on a single side."