Whenever something about software patents in general comes up, the majority of commenters seem to condemn them - at a minimum in their offensive usage. And a vast majority of commenters seem to be opposed to them at least to some degree.
So if as a general position you do not support the offensive use of software patents, why does the react license matter _at all_ to you? The only time it would matter would be if you would sue facebook for violating your patents. Am I not correctly understanding the license? Does it apply any other time?
Facebook made their own license for a reason. Compared to Apache, the Facebook license gives Facebook greater power in the user-developer relationship. They only give users use of React patents, but in return they demand protection against all patents from their users.
I'm not a huge fan of the patent system, but I'm even less a fan of hoisting Facebook into a position of even greater power over smaller competitors.
tl;dr: The clause isn't fair. It grants uneven protection. Their refusal to use a similar, existing, popular license that does grant equal protection is concerning.
I feel it's a little like this: https://www.xkcd.com/463/. Yes, the new license is providing explicit guarantees that do not exist in the MIT license. But... I'm not sure I like the thinking behind it when other licenses already address this in a fair way.
The MIT license says plainly that you have the right to use the software without restriction. To me, a layman, it would seem contradictory and unfair if the author later claimed that they held previously unmentioned patents that restricted your use of the software.
> Notwithstanding the foregoing, if Facebook or any of its
subsidiaries or corporate affiliates files a lawsuit alleging patent
infringement against you in the first instance, and you respond by filing a
patent infringement counterclaim in that lawsuit against that party that is
unrelated to the Software, the license granted hereunder will not terminate
under section (i) of this paragraph due to such counterclaim. 
As I read it, it only applies if you are the original instigator, not if they are.
The extremely clear and explicit purpose of the patent grant is to disallow "first strike" use, so this could only happen as a countersuit. How is that worse than the mountains of open-source code released with no patent grant at all?
Hope that makes it clear.
Edit: I've been drinking.
Except that's not what happens. What would really happen is that the patent grant would be revoked, but the license to the software (a matter of copyright) would remain in force. So they could sue you for patent infringement, just as they could always have done under most other licenses, but not copyright infringement. Under most other licenses they could even have sued you first, but they gave up that right. In fact, that's the only effect of the much-maligned patent grant. It's a pure giveaway compared to what the situation would be without it.
Let's change this to Facebook will sue you for patent infringement. This was never theoretical and it's rational for Facebook, if you read the post.
Nope, that wouldn't trigger the patent revocation.
Is the community changing towards a demographic intent on striking it rich, instead of the previous morals of openness? There are also more condemnation of, for example, the GPL now than there have been in the past.
So, for a while, everyone in upper management will continue with such policies as Facebook's, since they came up at a time where patents where anathema. We'll see if this changes when today's entry-level programmers climb the ranks–or if their views change over time, or if the latter selects for people of certain opinions.
The trouble is when you go to implement some of this stuff at work and get pushback from your team or higher-ups about the licenses for the software.
how is this different from pushback on (any) other issue?
Empirically, almost no large software companies have ever used patents offensively. They have repeatedly spoken out against the very idea of patentability for software (and "business methods").
this is the mutually-assured destruction analogy. If you can't get rid of them altogether you don't want someone being immune to them.