Am I the only one who feels that it's breaking the immersion of the game when you try and kill an NPC only to find out they were marked as "essential"?, I realize there are people who like certain characters to be immortal such as companions and important quest NPCS.How would you feel if we had an option in the settings where we can turn on and off characters to be essential? Thoughts?

Pretty sure that option is called mods. While I'm sure some people like to live dangerously, there wouldn't be an end of people whining how their quests are broken when so-and-so is dead. This is the safer approach and the ability to break one's game is left for mods.