no, but describing one's work place's only flaw as (paraphrased) 'we are so awesome that some good people can't hack it and leave' is.
"Not everyone is meant to be put outside their comfort zone...I've seen some good people just not hack it and leave" . In other words, people leave because the company's work is so demanding they can't keep up. Not that there's anything with anything the company does. No Sir. It is all those pesky people who can't stretch far enough.
Every company of 5k people will have definite dark sides that are not just 'some people are not suited to raise their game to our levels'.
Either don't go there, iow be diplomatic, which makes sense since you are an employee commenting on a public forum, xor give an honest unvarnished opinion of what those dark sides are.
Don't do these softball, 'we are so awesome that some people can't measure up and leave' stuff as the only 'negative' you can think of. Facebook has no other flaws (as a company to work for)? Seriously?
This is Hacker News, and soft soap (or what appears to be soft soap) will be spotted and called out. Think of it as feedback. Nothing personal :)
That said, I thought the rest of your answer was great ( I upvoted, fwiw) and conveyed something of what working for FB is like. This is just a minor blemish.