If the statutory rape involved force, I'm sure the sentence would be greater. But rape doesn't need to involve force. I obviously can't speak for Stallman, but

If the statutory rape involved force, I'm sure the sentence would be greater. But rape doesn't need to involve force. I obviously can't speak for Stallman, but I don't think he was trying to make the case that the guy was innocent, I think he was arguing that what he did may be okay in other jurisdictions and that it isn't technically assault. That's it. Stallman is usually very precise in his speech and doesn't go out of his way to counter potential misunderstandings of what says. I see that as a problem, but that doesn't mean he's wrong.