It's not against the law to hire someone to work on your home, however, you will get a professional job from a licensed contractor. Furthemore, if you obtain permits for the work that is being done, you will be protected against poor workmanship as well. A licensed person will have insurance also, in case he is hurt on the job in your home. If a person is not licensed and they are hurt..or worse..you will be personally liable for that.
In my professional opinion it is well worth the additional expense.