I have some quotes by Elie Weisel to contribute:
"Because of indifference, one dies before one actually dies."
"Indifference, to me, is the epitome of evil."
"Our obligation is to give meaning to life and in doing so to overcome the passive, indifferent life."
"We must always take sides. Neutrality helps the oppressor, never the victim. Silence encourages the tormentor, never the tormented."
OK, so the last one is more specific to acts of aggression but I do believe we must take sides. I don't believe you have to be overly opinionated but at least care enough about things to have position on them. I am very much for remaining open-minded but I don't think you have to choose between this and having an opinion.