Superman: Environmental Warrior, Counter-terrorist and anti-poverty advocate? That would be a pretty lousy movie. Superman isn't Jack Bauer, Al Gore or the Red Cross.
It is better to leave the real battles for the real soliders, and keep superheroes confined to stifling supervillains. To have Superman swoop in and single-handedly beat Al Qaida to a pulp would be somewhat disrespectful of those who are sacrificing. Wars aren't easily won ... and the movie wouldn't ring true because all the "crises" would still exist when people left the theater.
Also -- Superman IV tried to have Superman solve a modern "crisis". It turned into a preachy nuclear disarmament movie ... and the plot thusly sucked. Superman shouldn't get political. Even Christopher Reeve, who came up with the idea of making Superman politically relevant, said it was a HUGE mistake.
SnakeDoc