I think the real point Pete Seeger is making is that any good song is potentially "dangerous". It's the way you tell them.

I like that song Joe posted. I'd see it as dangerous three ways.

The man going over the mountain is in very dangerous situation. He's a rebel twice times over, liable to get shot by either side.

And I imagine it would still be a dangerous song to sing to some Southern audiences.

And at a deeper level, the song is saying there are times when your duty is to go against your own people and your own country. I imagine that in the days of the Vietnam War it could have been seen as very dangerous, very subversive.

And the times I've seen Pete Seeger in concert, those are the kind of issues that he'd bring out, singing a song that otherwise might have gone through as just a nice fun song.