I tried to run Tor browser bundle as a root but it it didn't start and I got the above quoted error message. I'm not sure why? and I'm also wondering if there is away to make that possible.
There is no advantage to using TBB as root, but there are significant risks.
It is a generally accepted practice that userland applications (ie: application that are not system services) should not be run using a privileged account. This is to help ensure integrity and isolation of potentially harmful applications from core system resources.
A browser in particular is a high value target for adversaries as browsers interact with unknown third parties. Despite the Firefox and TBB developers' best efforts, it is possible that there may be vulnerabilities in TBB. If an attacker took control of a system via TBB, the damage could be much much worse if TBB was being run as a superuser.