I think once we're past the unleashed dogs, he was tased for a much more egregious offense of resisting a lawful stop.
That's the real issue, and reason I haven't decided whether I'm outraged or not. He wasn't tased because of the dogs . . .he was tased for openly blowing off the ranger, who (assuming she told him why he was being detained, etc) had the right to stop him and give him a ticket and arrest him if he didn't cooperate. The problem is that tasers are meant to be a less-lethal substitute for a gun, and I think we all agree that shooting him would have been way excessive. (and yes, tasers can kill you if you have a pacemaker, as well as under other circumstances.)
But assuming she was smaller than he was (probably a safe assumption) she couldn't arrest him if he resisted, safely, without using the taser, and he'd already shown himself to be uncooperative. Just trying to handcuff him, or go after him with a baton would have been pretty dangerous.
And as much as I think "contempt of cop" is not and should not be a crime, blowing off a LEO who has given a lawful order, when you are in fact breaking the law, is the sort of thing that does need to have consequences. Otherwise, the enforcement of laws against minor crimes would pretty much become impossible, as people blow off the cops knowing nothing will happen to them.
The more I read about this the more I think the correct response would have been to call for back up. Of course, that assumes that a park ranger really has back up . . .
Edit: Dober, the problem I see with trying to arrest him first and tasing him if he resists, is that I imagine that he may well (and we don't know) have been substantially bigger than she. We don't know exactly what happened, which made it hard to judge, but I can understand that if he was larger and seemed like he might be aggressive, why she wouldn't want to (and probably shouldn't) get into physical contact with him.
Part of the problem with this is that we don't have all the facts.