There is a difference between being unable to do something about the problems of the world and being unwilling to even try.

It is interesting you mention Candide. You substitute the unrealistic optimism of Pangloss (Leibniz) for the disillusionment that caught up with Candide. If you no longer believe "we must cultivate our garden" at least do not try to dissuade those who believe we must try to eradicate the weeds growing in the gardens of the world.

There is a leadership vacuum in the U.S., at least in my view. What Voltaire ridicules goes on today. We face some very serious issues:

So, according to famed theoretical physicist Stephen Hawking, it's time to free ourselves from Mother Earth. "I believe that the long-term future of the human race must be in space," Hawking tells Big Think. "It will be difficult enough to avoid disaster on planet Earth in the next hundred years, let alone the next thousand, or million. The human race shouldn't have all its eggs in one basket, or on one planet. Let's hope we can avoid dropping the basket until we have spread the load." http://bigthink.com/ideas/21570

“I am only one, but still I am one. I cannot do everything, but still I can do something; and because I cannot do everything, I will not refuse to do something that I can do.” ~ Helen Keller