Ever actually look at a decapping die? The case is entireally enclosed by the die, if perchance the primer EXPLODES the primer cup and anvil are going to exit the bottom of the presses ram. Nothing is going to fly out up across or anywhere else. Its a primer, not a bomb.
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.
I have removed 100's of live primers as well using sizing dies as well as universal decapping dies. Never had one go bang. I also reused them all later with 100% success.