How can one assess whether they are a net-negative or net-positive for society?

This is a tricky question because 'society' has not always had the best Judgement about people (one might say that Society crucified Jesus thinking he was net-negative, but today we would say the opposite is true). A better question might be if societies Judgement is the only one we value. Generally, I would say that if a persons life produces less suffering in the world instead of more...more love instead of hate.... that is net-positive.