This kind of attitude is common among my friends who are more technical, but it can really damage communications with most people. "You're an idiot" doesn't just communicate "you're wrong" it says that you lack the ability to think at all, so all of your conclusions, whether related to this subject at all, are worthless. A good friend might take that in the way you intend, but there's no reason anyone else should. What is being called a Dark Art is something that Hermione would use; something that shows that you care about the other person's feelings, that you want to avoid causing pain where you can. It's a kindness. Sure, most of us can handle rough sports like intellectual boxing when we know what we're getting into, but most people aren't expecting to be sparring in a conversation.