Why I cannot use Scratchbox as root?
Scratchbox is intended to be used and be usable on developer desktops which are administrated by other people. For compilation root privileges shouldn’t be needed. It shouldn’t be needed for building packages either, for that fakeroot(-net) should be enough. Root is needed only when you install packages or run the installed software and even this only for very few system software packages. The main purpose of Scratchbox is building software. Additionally, running Scratchbox as root is an easy way to shoot yourself into foot, and as you’re compiling whole distributions in Scratchbox there’s a lot of software that might contain e.g. trojans. Sandboxing and faked root privileges make things a bit more secure.