Combat isn't always a life or death situation. I'll give you the Do part of your argument, because I'm agreeing with you on that, but in general you fight in martial arts. I'm not just talking about Taekwondo. You can call it sparring if you want, but if you look at it, it's still a fight. A practice fight, but still a fight.
Sparring is a game, and the name of the game is win points. Like any game, sparring has rules - no matter how hard and heavy you go, when was the last time someone was truly, seriously, intentionally injured in a sparring match? Bruises? Sure, all the time. Broken ribs? It's happened. Concussions? More common in competition than in class, at least in my experience. But serious injuries, inflicted with the deliberate intention to cause serious bodily harm, are not allowed by the rules.
Combat is something different. Certainly, the definition of combat can include conflict between individuals - which does, technically, include sparring. But the implications of combat are different, and the way I use the term combat does not include sparring as one of the options. There is only one rule in combat, and that rule is win or die. That's a totally different scenario than sparring in class or tournaments - even in Sabaki tournaments, there are rules that go beyond win or die, intended to maintain the safety of the fighters to a certain extent.
As an instructor - to get back to the topic as I originally posted it - I have a responsibility to my students, to protect them from themselves and each other until they reach the point where they can spar in a realistic and yet controlled manner - because sparring, as I said, has rules, designed to protect the participants. I teach my students to spar; I teach them to avoid combat whenever possible, through avoidance, through verbal de-escalation of potential violence, and so on. It is my responsibility to equip them, as best I can, to first avoid conflict that could lead to combat, but, if combat cannot be avoided, to escape as unscathed as possible.
Combat has a different set of rules, which are designed to bring victory to one side, and defeat to the other. Defeat does not have to mean death for the defeated - although it can - but losing a sparring match, no matter the rules or the stakes - is not, or at least should not, be a life or death, win or die situation the way combat is. If that's what you're training for, join the armed forces, because they need you - people who are truly willing to die for their country are an asset beyond measure. But if you're training in MA, and you think that sparring and combat are the same thing, you need to sit down and rethink what you're doing, and why, and then have a long talk about the subject with your instructor... and then you need to go talk to some veterans from the armed forces who have seen actual combat, or some LEOs, and find out what the differences truly are.