In the spirit of Christianity, offer the other cheek so to speak. I think the best thing is to ignore it. It sounds like they're looking for a fight. And maybe the thing to do is to unfriend them. They are being un-friend-like. If they loved you as a friend is supposed to love a friend, they wouldn't write such things.
If they call you on an unfriending, you can explain it simply that "You're my friend/brother and I love you, but lately you've posted some things that are very hurtful to me. I know Christians aren't perfect, I know I'm not, but I would prefer not to be put down by people who are supposed to love me." But that is only if they call you out on why.
Sorry you have to deal with this. It's a tough one.
Rae (27), DH (26), Lucas (6/3/12), #2 due in December