Why does everyone have to be a showman?
Because he's putting on a show. Quality of the presentation matters. A lot. Especially if you are trying to persuade others on a topic they are not familiar with. If he's not good at presenting then let someone who is good at it do presentation. I realize he is sort of the figurehead for the movement but part of being a good leader is knowing your limitations. He clearly is not very good in front of a crowd in a context like this. Maybe he's better speaking in other formats but he wasn't good here. Geeks tend to be uncomfortable with the truth that sometimes image matters. Your message isn't just what is being said but how it is being said and by whom. A stupid message well delivered will be far more convincing than an brilliant idea poorly expressed.
Reagan as a professional actor was better at looking "Presidential" than any other US President but that doesn't mean he was the best President of all time.
True but it's a LOT easier to get people to listen to what you have to say if you are charming and persuasive and look the part of a leader. RMS is certainly not charming and at least in this talk I don't think he was very persuasive either and he never has looked the part of a leader. The best leaders aren't always the most telegenic but the ones that aren't usually know that and stay away from the camera. RMS should play to his strengths and it seems that TED talks are not one of them. Frankly as a supported of free software I'm kind of embarrassed that this guy gets the platform. I strongly suspect that a lot of people came away thinking RMS is a weirdo with weird ideas that don't apply to their lives.
It's better for everyone if he's just himself laying out the information to be taken on it's merits instead of trying to sell something or put on a show.
That sounds like it should be right but in the real world it doesn't work that way. He is "selling" an idea and there are ways to do that that work well. Showmanship is a part of the equation. I more or less agree with his thesis but the argument he presented in this TED talk wasn't logical or systematic or credible if you aren't already convinced. If you are going to make the argument that "you control software or software controls you", you're going to have to explain that. It's not axiomatic. It was poorly presented and really didn't understand the audience. He clearly didn't spend time rehearsing or preparing and for a talk like this you have to spend a HUGE amount of time rehearsing and polishing. The reason that politicians sound so polished in their stump speeches is that they've given that exact same speech hundreds or even thousands of times. They know exactly the right cadence, how to deliver the jokes, how to make it sound off the cuff even though it isn't. This takes practice and lots of it.
Remember that he is making a political argument. He's trying to convince and persuade people of an idea that they are not forced to go along with. Simply having the superior argument is not even close to sufficient. You can still lose even if you are right.