In a sandbox game where I can go wherever I life from the beginning there is a risk that I may kill every person who might give me a quest later on including the end boss. If I were to do that, it would kill every quest in the game including the ending. I would be left with no game at all.
I have no problem having essential characters which can not be killed until after I have no need in my game for that character anymore. The alternative, as in Morrowind, is that I kill them and get a little pop up message saying I have severed the the ties or whatever of prophesy which is every so maddening and causes me to have to go back to a former save before I killed them. Of the two....I'll take the essential, non killable characters.
The only other way around it is to make the game so linear that I won't run into them until the time is right which makes it no longer a sandbox and takes away freedom to roam.
Seems if I want that....I'll run off and play some other game.
I can definitely see where people who share your point of view are coming from. No one likes having their game ruined because you killed someone you didn't know was supposed to die, but that's what those messages are for, saying you've messed your game up, ala Morrowind.
But, and hear me out, that's not the point.
The point isn't that I want to just kill everyone I see. The point is, is that I can kill everyone I see. I don't want to go around slaughtering masses of people. That's not how I roleplay in TES. I RP very seriously and killing sprees aren't on my agenda. The point is, it adds a level of tension and realism that was non existent in Oblivion. Like I replied to one post in this thread already, the first time I met Dagoth Fyr, I literally crapped my pants because of the tension. If I let that trigger slip, bam. I'm done. Game over. That makes it REAL. Knowing that all I have to do is "wait" 9 seconds for him to regain consciousness after I slaughter him with a massive battle axe absolutely
ruins immersion for me. Just KNOWING that I could kill him makes it so much more realistic. It's not always about "hey, I want to kill this guy and ruin my game." It's about knowing if it came down to it, it could happen.