On the one hand, what people decide to do is their own responsibility. Dan Sperry shouldn't have to worry about people copying him poorly, because he's not telling them to. He has his own very unique character and I don't think anyone else could pull off his material quite like he does. If someone does try, and fails miserably, then they must deal with the consequences of their lack of foresight and originality.
Of course, on the other hand, I have to deal with the image those idiots give to magicians, so I'm a little torn on the idea. For the most part, though, I think a performer shouldn't worry about other people copying him. Otherwise said performer will be censuring his creative freedom, and I'm against that whole heartedly.