A well supervised day at the track is in most cases going to be safer than the drive to the facility. However, as with most things in life, strange things can sometimes occur. Your well focused and instructed driving might be flawless, but some small part may fail and send you on a different journey. This can happen on the street or at the track, but because of the higher average speeds experienced at one of these events, you should take propper precautions to make yourself safe. If something happens, you won't have the opportunity to say, "gee I guess I should have had a good roll bar installed".
It is very exciting to drive your street car on the track, and I highly recommend it, but you need to prepare yourself and your car for the experience. Safety should be the most important consideration. Only then can you be confident enough to drive your best.
People that enjoy tracking their car and get more serious about it ultimately end up with a non-streetable dedicated racecar. Whatever performance enhancements are made are usually more than equaled by safety improvements. It just makes good sense.