We already do, or at least my classes do. When we cover a subject, we never stick to the text, we have research and find out what exactly the circumstances and the times and what happened, be it good or bad. Like George Washington's Missing Slave Ad, or that Ben Franklin spent most of his time in France getting laid. For a more serious look, we covered how white encroachment destroyed Native Americans and how we continued to give them unfair rights up into the modern era. They don't focus on the negative entirely. It's a comprehensive thing, you learn the good and the bad. So I think yes, we should learn dark and light sides respectively. This way people don't have a narrow and close minded view from either perspective and can g into the world with an expanded knowledge base.