"Knowledge is preferable to ignorance." - Carl Sagan.
Delusion is always a mistake because it opens the door to more severe delusions. As Bill Mahr would say, once you believe that a man came back to life and floated up into the sky, anything you base on that belief could and probably will be flawed. Your higher level beliefs will trickle down, so to speak, and effect your lower level believes all the way through your entire being.
If you're thoughts, beliefs, and actions are not aligned with reality in the best possible way, your results will suffer. Since greater accuracy means greater fitness for life, your internal model of reality must match up with actual reality.
Despite delusion being wrong because it separates our beliefs from the reality in which we must live, there is benefit in developing the habit of seeing the positive side of things.
It's okay to be positive. After all, there are two sides to every coin. And there may be value in filtering out input that hurts your sense of peace and well-being. If there's nothing you can do about it or there's nothing that should be done about it, such as national news events that seem to effect your emotions negatively, then press the off button or change the channel.
First you must be grounded in reality. If there are real problems that need to be addressed, then by all means they should be addressed and not ignored or "left to God." But after giving a problem the proper amount of attention and finding there isn't much you can do about it, just let it go and have some peace of mind. For problems that you can do something about, make a plan, work it, and try to have some peace.
As for contribution, since we're all part of this system we call life, it makes sense to take a top-down approach rather than drawing imaginary lines that separate us and cause "in group" mentality based on species, race, religion, nationality, borders, political affiliation, sexual identity, etc. In other words, the enemy is not the out group because there is no out group.
Think about the very nature of humanity. We bravely explore, pushing the boundaries of what's possible. We learn and progress as a whole. We create medicines and vaccines to reduce suffering and increase lifespans. We come to the aid of others in times of need. We are the masters of our environment and our own fates. We are the species with intelligence and forsight. All life is our responsibility. Too many people look to God to clean up the planet and take care of wildlife. So far it seems if there is a God, he's not doing a good job. So life depends on humanity.
What pervades humanity in the form of ideals is very straighforward. Do unto others as you would have them do unto you. Equality, fairness, life, liberty, freedom, democracy, love, compassion--they are all ideals that have grown because they have proven to bring more happiness and less suffering to the largest number of people. And with the growth of technology and communication, the boundaries that separate us humans from each other are constantly being pushed back. We are becoming, over time, a more congruent "organism."
Whether on a small scale or a large scale, life is about the struggle for resources. All life has its basic needs. Some want more than they need. As such it becomes appearant that conflict must exist in its many forms--eating and not being eaten, war, revolutions, competition for resourses and ideals on all levels. Without conflict, change would not occur. These changes sometimes are beneficial to the whole and eventually become a part of the entire system. Often they are not and are "weeded out." Sometimes these revolutions destroy the whole, as is the case with cancer or nuclear weapons getting in the hands of an angry group. Evolution does not just apply to living organisms, but also ideals and attitudes.
War and conflict is not so terrible a thing except where it threatens the wellbeing of all humanity. Revolutions and changes in the paradigm occur but almost always for the betterment of the whole. Life will only improve over time unless some great event stops it altogether such as nuclear war or cosmic disaster. If we run out of oil for energy without finding adequate alternatives or the global climate changes drastically, it will serve as a lesson to those who do survive and life will continue on but so many will suffer. And that is why we must take action.
So it makes sense to have faith in the general goodness of people. We will move towards improvement over time because good usually wins over evil, ultimately increasing good and reducing evil within the system as a whole. And most of the evil in the world occurs as a result of not having an accurate mental representation of reality.
What is truly important is being aligned with the general goodness of humanity as the responsible leaders of life. Therefore, anything that's not aligned with what is good is not worthy of your time and energy. In the words of Gandhi, "Be the change you wish to see."