From watching the Video I can see why they cut his mic. He was asked to stop and step away, but I also note that in political discussions people can get very heated but from where he currently was he was in no way making threats or advancing.
All in all I think that physical restraint and tazering was way to far, but Im also one of those crazy people who believe in free speech and all that crazy jazz.
(Also, on the note about the applauding of the removal of him, it makes sense that the audience would want someone who seems to be irritating to shut up but just moments later you heard crys and outrage from students who may have been happy moments ago that his mic was shut off)