The way the father describes it, it sounds like the guy was verbally abusing a child, and if his description were accurate, I'd be almost as upset at him as the preacher.
However, what the video shows is really no different from the street corner preachers you can see in any busy downtown area, except he has a microphone. He was a fair distance from the child. There were plenty of supportive adults nearby.
I don't know that I would have filmed it, but with my son, under the same circumstances, I would probably have stood by and waited to see his reaction. I would bet on his courage over the preacher's.
I don't think it's a parent's job to jump between their children and everything they'll see in their lives. Protect them from actual danger, sure, but the girl wasn't in danger. She wasn't showing any outward signs of distress. The father was close enough to intervene in a moment if things took a bad turn. It's not his job to keep her from seeing the hate in the world. It's his job to see that she can handle it well. She seems to have done so. Even the fact that she said later she was scared isn't a condemnation. Kids are scared of lots of things. A little fear isn't always a bad thing. She's learned that she can stand up to loud, scary men who want her to do what they say. Great lesson.