If you are employed at will, your employer does not need good cause to fire you. In every state but Montana (which protects employees who have completed an initial "probationary period" from being fired without cause), employers are free to adopt at-will employment policies, and many of them have. In fact, unless your employer gives some clear indication that it will only fire employees for good cause, the law presumes that you are employed at will.
http://www.nolo.com/legal-encycloped...ion-30022.html
Once again, your ignorance is proven beyond reproach.