>Is that the "why"? If so, what does he mean by it? Meaning: What is the "danger" that Matt says Automattic will never run into, but that WordPress users will run into?

He answered that already. He doesn't believe there's much (if any) danger, but:

"we have a lot of problems to tackle, and convincing the world that Facebook’s patent clause is fine isn’t ours to take on. It’s their fight".

So what they don't want to "pass down to [their] users" is not something they believe is an actual danger, but the anxiety about the licensing that users would face and the arguments etc that will erupt over this.