I learned a great deal from listening to a recent Radiolab podcast about Beethoven, but I didn't learn anything about Beethoven from it. When the hosts confessed their mutual dislike of Beethoven, and then suggested that the Beethoven "we" know might not be the Beethoven that he wanted us to know because of the metronome markings, I wanted to stop listening, but I continued (it's only an 18-minute podcast). Matthew Guerrieri's voice popped into the discussion, and there were elements of sense that came up concerning the tempo a person might choose when playing music in different acoustic environments, and the fact that Beethoven couldn't actually hear his metronome. I know from experience that composers almost pick tempos that are too fast for fast movements, and I have never taken printed tempo markings (even mine) to be anything aside beyond suggestions. Italian words are nice and vague. They suggest character, and that's what music is all about.
The hosts had a string quartet play some excerpts from Beethoven's 5th and 3rd to demonstrate how exciting it is to hear Beethoven played, with a metronome, at a fast tempo. It would be very difficult for a whole orchestra (including the bass section) to play at such fast tempos without scrambling around, but the hosts didn't touch that subject (it would muddy their argument).
After these 18 minutes I now understand why so many New York musicians tend to favor fast tempos. They think that it makes music more exciting. Perhaps they think it's what people want to hear. I noticed it 30 years ago when I was at Juilliard, and I notice it in many recordings I hear from New York-based ensembles. I noticed it last week when I heard a New York-based woodwind quintet play a concert out here in the "hinterlands."
I think that tempo is subjective and relative, and that there is a whole world of musical excitement that has little to do with speed. I hope that Radiolab keeps its distance from musical subjects in the future.