The best way to drive this point home is the example of LifeLock's CEO. LifeLock is an identity theft protection company that used to run an advertisement with the CEO's actual social security number. His identity has been stolen at least 13 times.
These companies cannot actually prevent identity theft. They can help you clean up the aftermath, but the only real ways you can decrease the odds of identity theft is to practice good password management (i.e. use a password manager and a unique random password for every service) and freeze your credit report. This won't necessarily prevent all identity theft, but it's the best thing you can do to prevent new accounts being opened in your name.