We have been wanting for ages for all the differences, inequalities, suffering to disappear from this world. But if that utopian dream ever materialises, what a dull, drab and monotonous place this planet will be. The absence of wars, suffering and poverty will make peace, happiness and plenty erode their meanings. When you are always happy, you don't understand what happiness stands for.
We may despise the negative aspects of our environs and make efforts to diminish them. But for the sake of making our existence more meaningful they should never be eliminated. A little of evil is needed to make the good feel better.