Every decision a person makes stems from the person's values and goals. People can have many different goals and values; fame, profit, love, survival, fun, and freedom, are just some of the goals that a good person might have. When the goal is to help others as well as oneself, we call that idealism. My work on free software is motivated by an idealistic goal: spreading freedom and cooperation. I want to encourage free software to spread, replacing proprietary software that forbids cooperation, and thus make our society better.
Without absolute certainty, what do we do? We do the best we can. Injustice is happening now; suffering is happening now. We have choices to make now. To insist on absolute certainty before starting to apply ethics to life decisions is a way of choosing to be amoral.