Keeping calm will certainly help people who stutter, but it is impossible to be calm all the time while speaking. If you observe people talking, you will see that they express many emotions because speaking is a complex and emotional behavior. Moreover, emotions are not under our control, so for someone who stutters, it will be very difficult not to feel emotions while speaking, considering their traumatic past with stuttering. But without a doubt, it will help, but not cure it completely. Besides, there is another factor that I mentioned.