To be honest, I'm really not qualified to comment on this topic, and my opinion may change over time as I spend more time thinking about this, but I'll at least share my gut reaction to it.
To me it seems like a defensive play by Facebook and it doesn't worry me, personally. If I could choose, I'd probably prefer they use a more traditional open source license, but they're of course free to license their software however they like. I still happily use React and don't plan to change any time soon.
Not sure where that puts me in terms of "for or against" 😄