Here is a better question for you...

Why do we really need banks? I can't think of one.

What is the only difference between a bank and Bernie Madoff?  A bank actually uses the ponzi scheme money to make more money for itself while Bernie didn't.

If you like being screwed every possible way that you can imagine then stick with supporting our current banking system.  However I wouldn't go around spewing really ignorant questions like why do we need Bitcoin? Why do we really need Amazon?  Did we really NEED smart phones when they first came out?  Is social media necessary?  Do I really NEED to see pictures of you eating or working out?