You need security. You don't realize how much you depend on it. You trust that the bank is secure, otherwise you wouldn't deposit your money there. You'd be amazed just how easy it is to hijack a TCP-connection and restart an SSL connection forcing the browser to resend your credit card number to him instead of the server. Say you need to send passwords to your coworkers via email.
Email is far less secure than most people think.
Anyone can read your email, whether or not they have your password won't detain them. Well the answer is simple. Strong encryption and other security measures are available. There's a very dangerous race condition between those two players. If it's just a little bit off, you're at risk.