The idea that all we need to solve the world's various problems is "love."
That's like telling a depressed person all he needs to do is be happy, or that an anxious person need only calm down. It shows an ignorance of the issues at hand and is empty of any utilitarian value. In fact, it serves only to give the utterer a false sense of profound insight. "Why, look at that," they pedantically muse, "I have resolved dilemmas that greater minds with greater drive have failed at!"
Also, the trope of the child confounding the learned/wise.