It is a good idea to ware safety glasses. Even tho it is unlikely a primer will even go bang does not mean you should tell someone to disregard common safety equipment that should be used when doing any reloading.
Never "told" anyone to do anything. Just stated the fact that the depriming die encloses the case and that the primer cup and anvil will exit the bottom of the presses ram.
Do it behind a steel shield if you wish.
Myself I wear safety glasses, and have since perscription glasses have been safety. I cannot remember not wearing glasses, probably started at around 2/3 years old. I do however remember glasses breaking tho.