The most valuable asset that any licensed professional has is their license to practice in their chosen field, and of course teachers are no different in this regard. No matter how good you may be in your career, it makes no difference if you lose your license to practice. All professionals - doctors, accountants, dentists, nurses, etc. - of course are terrified by the prospect of losing their professional license due to some past transgression, but teachers especially face unique circumstances when it comes to past criminal conduct.