I think most friendships are less unconditional than family relationships.
There aren't many friends who can have blazing rows and fundamental disagreements about things and still preserve a very close friendship.
I have one friend who I can say anything to (even about her children, her interfering with her DIL and grandson etc.), and I know we won't fall out. But that's because we are such close friends, she feels like a family member, iyswim. We're part of each other's life furniture. I've only got one like that though.