Earlier quoted context omitted.
"Facebook is granting you additional rights on top of the BSD license. In the worst case, where you do something that causes the patent rights to be revoked, you're still left with the same rights you have under the BSD license. This is unambiguously safer to use than if they had released it under a vanilla BSD license. As for why Facebook did this, they're most likely trying to give away additional rights while stil…
This is actually well settled law. I'm not sure it is, and I'd argue the situation is unclear. I'd be keen to see any examples though – it would be awesome if there was something to fall back on. All I can find is evidence that it would be at best very risky to rely on an implied patent grant. For example, it's considered unclear enough that the ClearBSD license was explicitly created to clarify that it doesn't offer…
I wouldn't. What you've quoted is Larry Rosen's view. Larry is a wonderful guy, but his views are pretty far outside the norm for open source lawyers.
To start "If software is licensed under the BSD without forming a contract between licensor and licensee, the extent of any patent grant is at best ambiguous."
This is now settled since he wrote this. It is in fact a contract, that, if breached, leaves the licensor without a copyright license (causing both infringement of copyright and breach of contract).
So you don't have to worry about this.
The latter is a real issue, but one that most explicit grants don't solve either.
In particular, apache/et al have explicit grants do not cover modifications by others that suddenly encompass patents.
So you aren't any better off there either :)