I think that PowerPoints have their proper place in speeches. However, we are yet to find it. PowerPoints are great for helping people connect ideas from the speech to visuals. PowerPoints are not great at explanations of ideas. For very complex speech topic or small audiences where the details are important a PowerPoint is not needed so oversimplification can be avoided. However, for large audiences or a speech where every detail is not emphasized a PowerPoint is a helpful tool to draw attention to the main focus of the speech.
I see this apply mainly at church. The use of helpful pictures, fill in the blank notes, and other useful PowerPoint slides are very helpful to better grasp the material of a message, and, if given by a well spoken Pastor who knows the content and context, it can be engaging and more applicable than if there were no slides.