well, off i understand you correctly, you want to just stay logged in and never bother with the password in your device? That comes with a heap of problems:

• what if someone else gains access to your device, they’d have instant access to all your accounts
• what if your device died? If you don’t know the passwords you can never log in on anything else.
• if you whitelist cookies those sites could track you across other sites, thus INCREASING your attack surface