That goes for almost any object. And if you had unlimited resources your argument would be valid, and we'd buy infinite amounts of everything 'because it is better to have it and not need it'. But we do not have unlimited resources, we can not buy everything that would be 'better to have and not need' so we're going to have to think a bit more seriously beyond 'but it is nice, no?'.
Put very simply the question is: how much does a human life cost? How many lives do you safe when you invest another billion in healthcare? How much when you put it in police, fire brigades, education? And how does that compare with this project? I do not know the answer, but I can tell you it is more complex than 'but would you rather have it and not need it or need it and not have it?'.
You are just trying to avoid the problem by deflecting with another problem.
The question was very simple, when you have the possibility to obtain an object that "could" be of use in the future but you are not certain of it, would you rather have it or discard it and take the risk that if the moment when you need it comes you will be unprepared.
And about a life's worth, is a question as old as humankind itself.
To answer this, one must first ask to oneself what kind of life you deem worth.
You tell me ALL life is equally precious. To this I ask you, If you have to choose to save ONE life between two. In a situation where you CANNOT save both.
Who would you save, a convicted murderer or a nobel price scientist?
Following your statement, you would consider saving the murderer, since for you all life's are equal.
Sorry, but that is not the case unfortunately.
Some people go as far as to claim that they would rather save their dog rather than some stranger dude. So, what are you going tot tell them?
Personally I would rather like not having to make that kind of choices in my life, sadly, this kind of choices are made all the time without you even being aware of it!
But between deciding to build a fighter that will help me in defending my interests and those of my fellow countrymen, and just abandon any kind of sovereignty and let myself as well as others be told what to do and what to think. Because "war is bad". sorry but I would rather build the fighter, in hopes that I never have to actually use it.