Just because it is "facebook" it doesn't mean they aren't doing something dumb. Otherwise there wouldn't have been so many news about facebook hacks where they leak user data.
But also you have to consider the target audience of Facebook. There is a lot of dumb people who don't realize the difference between upper and lower case in a password, specially those on phone where for example the first letter is capitalized automatically.
haha, no I did not paste link about facebook to justify it.
In fact, I would never think about that kind of "user-friendliness". You cannot imagine my surprise when I found it for the first time - I realized that I may log in into one of online shops with CAPS LOCK. I was really surprised, I had feeling like
any password would work. Then I found out that some treat it is as a
feature, not bug.
On the other hand, I think that now smartphones are
smart enough to detect password field and disable autoCaps.