Spoilers for a 13 year old game that got retconned anyways

For those who don't know, at the end of Fallout 3 you have to go into a heavily irradiated room to prevent a big water purifier from exploding. Your character will die but your act of self-sacrifice gives everyone in the wasteland clean water which had been very rare up to that point. However it's been previously established (explicitly and several times) that supermutants are immune to radiation, and the game has a very prominent supermutant companion: Fawkes. You would think you could just ask Fawkes to go into the radiation chamber, but no, you get this incredibly stupid line and are forced to kill yourself. Fawkes up to this point has been very selfless and one of the kindest characters in the game.

Like how do you fuck up writing your game so badly this situation is even possible?!