I don't know why people are saying you can't go back. You've ALWAYS been able to 'downgrade' to a previous iOS. So unless there's been a fundamental change with iOS7, I'd imagine that you still could. In fact there are videos and guides to show you how to do it. Here's how I've always done it with previous versions of iOS (or when installing a beta version of a new OS).
Go online and download the relevant .ipsw file to your computer (less than a minute of Googling and I've found them
Open up iTunes
Plug your phone in
Hold down the Shift key, and click 'restore'
iTunes will then prompt you to select the .ipsw you wish to use. Select the one you downloaded.
Your phone will now restore itself with iOS6.
Here are the links to the .ipsw files you need (note that these links will automatically begin to download the file to your computer):iPhone 5iPhone 4 & 4S
You just need to bear in mind that Apple won't be updating iOS6 again, and it'd be a good idea to stop any automatic updates otherwise the phone will just download the latest version of iOS7 again (which, incidentally looks like Jonny Ive has let his 4yr old kid loose with the crayons) and you'll be back to square one.