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.
Frankly they get bonus points in my book just for the mere act of divesting from something Facebook owns, so that would've been a good enough reason for me. But hey, they also get to retain their right to sue Facebook if needed.