First, let's address the safety issue. Compared to other recreational sports, strength training has an incredibly low rate of injury. People think of soccer, for example, as being safer than weight lifting, but participants average 6.2 injuries per 100 hours of playing soccer versus 0.0035 injuries per hundred hours of weight training. Even badminton has a higher rate of injury than weight training, with 0.05 injuries per 100 hours of play.
Now think about the safety of specific lifts. If you're going to get injured while lifting weights, it's probably going to happen when you're trying to lift too much weight and you lose control of the bar. A Bench Press would be the worst lift for this to happen on, since a loss of control means the bar crashing to your chest, and possibly remaining there if you have no spotters or bad spotters. If you go too heavy on a Deadlift, on the other hand, all you do is drop the weight. A worst-case scenario would be the weight rebounding off of the floor and smacking you in the shin.
So with the Deadlift's potential for catastrophic injury now realistically assessed as being very close to 0, we address the issue of "messing up your back." Yes, your lower back will probably be sore after a workout involving Deadlifts, but only in the way that your chest is sore after a workout involving Bench Press. A correctly executed Deadlift will NOT injure your back. Ever.
The only way to injure your back by Deadlifting is to perform the lift incorrectly, in which case you're not really doing a Deadlift, after all. In a correct Deadlift, your back stays straight throughout the entire movement while you lift the weight by extending at the knees and hips. If your back stays straight, you can't hurt it. Period.
Since correct form is the most important factor in safely Deadlifting, you should learn all you can about correct form. Read online articles. Watch video of correctly performed Deadlifts. Ask a personal trainer who has a Powerlifting or Olympic Lifting background. If you're serious about strength training, buy Starting Strength and read it cover to cover. Do whatever you need to do to feel confident in your form. If you have the equipment, periodically video yourself performing the Deadlift so you can check your form. You can even post the video online and ask for feedback on your technique.
"You Deadlift like a girl." "Thanks!"
The Deadlift is an extremely useful lift that has gotten a bad rap thanks to idiots like this guy. Correctly executed Deadlifts are one of the best ways to build strength in the series of muscles known as the "posterior chain": glutes, hamstrings and back. They also teach you how to correctly and safely pick up heavy objects from the floor. The Deadlift is an extremely useful exercise for everyone from the 17 year old who wants to get stronger for sports to the 70 year old who just wants to be able to perform everyday tasks without pain.