I don't think you can avoid having passwords, I'm afraid. You can however have a blank password for all regular users (which was the most usual password in the world a couple of years ago). This is not recommended, as it opens your Mac up to all kinds of attacks, but if you're behind an external firewall (like a router with built-in and enabled firewall), don't have any sensitive information on your Mac and at least keep a good password on your admin account, you might get away with it... 🙂