So I coincidentally talked to my brother a little while ago on the phone to catch up on something else, and so I brought up the subject. He had a pretty balanced view on the taser thing.
For one, they are used on violent suspects, which this guy was not to what we can see. They can be used on non-violent people who resist moving or arrest, which this looks like the case, but that's still somewhat controversial. For now, it is considered a legal and recommended part of the enforcement code.
As for the suspicion that a person who is tasered cannot get up and walk on their own, that's a load of crap. Tasers basically apply a shock for about 5 seconds and their effects wear off immediately once the voltage stops. You should be able to walk around as if nothing happened to you. The immediate removal of any effects of the taser is one of the reasons it is most often used as a non-lethal weapon. Pepper spray takes about 40 seconds or so to wear off. And unlike a club, a dog, or some other means of force as was standard operating procedure in the past, a taser is far more humane and leaves no after effects (... save maybe in some edge cases where someone has a heart condition, etc., as you bring up).
People volunteer to be tasered all the time in demonstrations. An alternative method to get someone to comply in moving on their own is to apply something briefly painful at pressure points -- such as sticking a thumb on a person's neck in the right place, etc. Basically, the idea is to apply a form of momentary pain to get the person to comply in movement. Twisting arms, etc., is the same.
Apparently, dragging the person is considered more harmful for both the back of the dragger and the involuntary friction and banging around of the dragee -- which is why that is generally not used under the circumstances.
From what it sounds, his cries of pain seem to be a bit of an exaggeration in comparison to what pain a taser really inflicts -- but then, I haven't tried a taser myself and don't really plan to. (Though I have been hit by rubber bullets when caught in a crowd dispersion cross-fire at a Berkeley protest -- it sounds like I would have preferred an accidental taser.) And yes, his cries of pain do bother me. But from what it sounds, I would have every reason to believe that a belligerent guy who refuses to move with an audience of people around him might do everything possible to exaggerate his circumstances. Not saying he wasn't in pain, but I am suggesting there's a high likelihood some dramatic acting was in effect to elicit the responses that you and I had.