Well, the building has generated, generates, and will generate billions of dollars to its community if not an entire country. During the years, Notre Dame has provided to more people what a billion of dollars can't provide if not for a very limited time and for a limited set of people. There are about 9 million people living below poverty line in France (1,000Euros or less a month). A billion dollar would generate about 110Euros per person below poverty line. Once. A billion dollar invested to reconstruct Notre Dame will provide much more money to the community each year, for a few hundred years, therefore limiting poverty and increasing the numbers of jobs.
Also, Notre Dame is surrounded by homes and offices. Part of their high value is because they are at "walking distance" from Notre Dame (among others). Without a fully functioning Notre Dame, thousands of building would lose part of their value and appeal.
In addition, yeah. Lives are lost every day, and suffer every day. Take a snapshot of today's earth. All 7.5 billion people. You can be sure that in 120 years or so, all of them will be dead. A few other billions will keep dying, most likely until the end of times, exactly as many billions died in the past for whatever reason. What remains of those billions of people? Their work, what they left behind them. Notre Dame is one of the things that Parisians left us, leave us, and will keep leaving us (until its destruction). They left it us during several wars, governments, poverty, richness, empires, and revolutions. All the poor in Paris are represented by that building. All the rich in Paris are represented by that building. That building is one of the things that remain of all Parisians that lived, worked, and died since the day the first stone was set. A brutal emperor was crowned in there and I walked in there. We are equalized in there as that building is what remains; neither Napoleon or myself will outlive it.
So no, for a society which is fairly in good shape, a building like that one is not only a good investment, but a fundamental functional element.