There is a majority of people, in every nation and culture, of every religion, who believe that there will be a time when this world will become perfect, when there will be no disease, or death, or unhappiness, or wickedness. That is a nice idea, and has for a very long time motivated and inspired to uplift the ignorant, but if we think upon it for only a moment it is clear that this cannot be so. Swami Vivekananda teaches that good and evil are like two sides of a coin - neither are the coin itself, neither have any value, no meaning without the other. Life itself is a struggle to maintain itself: without food, water, air, or other necessaries, life fails - even as without two sides, the coin fails to be a coin. It is the struggle of life which gives it meaning. The way a life is lived matters a great deal more than what is purchased by it: a coin, once spent, will be spent again and again (if it has true value). A counterfeit coin is thrown away as soon as it is discovered to be valueless, meaningless.
What is this manner of living which gives value and meaning to life? It is Karma Yoga - the way that we yoke ourselves to the results of our actions.
There are those who do good for themselves, to the detriment of others - or good for others, to their own detriment. Such good is not without merit, value or meaning. But more merit, meaning and value is found in those who do good for themselves, and no harm to others - or good for others without harm to themselves. This Ahimsa is the result of the training and practice of Karma Yoga: and it permits the ultimate act of doing good, without understanding difference between self or other. Swami Vivekananda said that the Buddha Gotama taught the training and practice required for such Karma Yoga through an application of logic to ethics.