When we make new friends, how often does it happen because we said "Shall we be friends?" I imagine the process of friend-making should go something like this:
Person A: I like you. Do you want to be my friend?
Person B: Okay, let's be friends.
Person A: Hello, friend :)
But this is the oversimplified version. Really, even though we don't say it, what we mean is this:
I think I like you. Let's be friends for a while, and then if we like it we'll be friends for a bit longer until we get bored or until we stop liking each other. How's that sound?