It comes down to you simply have to know what you are doing. The Glock is a great gun but it is not as forgiving as other types. There is no safety to disengage, no hammer to look at to see if it is cocked it is a fighting pistol, point and shoot and may not be for everyone or anyone who does not want to train with it.
The Washington D.C Metro P.D. switched to the Glock in 1989 and was supported by officers and their FOP.
Almost immediately they began to shoot themselves and each other. In the decade after adopting the pistol there were more than 120 accidental discharges which resulted in 19 serious officer injuries. Police mistakenly wounded nine DC citizens and killed one. This resulted in city government paying out millions in damages however they did not blame the guns. After investigating the incidents they found it related back to three factors.
The department, responding to turnover and rising crime, hired 1500 new officers in just 18 months. It then failed to train many of the rookies. In many cases the rookies only received three days range time instead of the normal ten. They simply rushed them through to meet the numbers they needed. The final factor is that they issued the easy to fire Glock in the hands of every one of the untrained officers without further thought.
The pistol is an excellent first gun as it is simple and light, but without the training to go with it a new shooter is probably more likely to make a dangerous mistake with it as compared to other firearms.
I have never heard of a Glock discharging while in the holster so if anyone has a link to something I would appreciate it.
In November 1990 and officer with the Port Huron MI. PD was in his patrol car when her removed the gun from its holster. (Goes back to leave the damn thing alone until you are ready to use it but anyway...) as he did so the gun discharged shooting him in the foot. The following year he sued the gunmaker alleging the unusual "trigger safety" was inherently dangerous.