What can we call the mistaken belief that something can't be measured?

If the person cannot bring an argument for the unability of measurment then i guess it could fall under the arument of ignorance "I, and maybe we, don't know if, then either it's impossible or everything is possible". In this case "I don't know how to put a value in human life then it's impossible". This my best shot so far but it has some limits i guess, usually the argumebt of ignorance is used in a debate where facts have a important place as "Do Alien already came to earth" or "Do vaccines work ?". In this case the argument can take the following forms : "We cannot proove that aliens didn't land in ancient greece therefore it can be possible", "We cannot say for sure that nobody has ever died because of a vaccine, therefore we can't proove that vaccines are dangerless".

In this case (the value of a human life), i think that the debate deserve more than a fallacy accusation, the value of a human life brings so much ethical mindtwisters (for ex. The tram dilemma) that bringing the "ignorance fallacy" on the table seems a bit easy and lazy.

To answer this we would need to explain what the fallacy is here, and simply saying "I believe this is wrong" doesn't make it a fallacy.

I think you need time to develop what you think is wrong fundamentally wrong here, at a philosophical, ethical and utilitaristic level (i guess utilitarism is your path to claim that human life has a measurable value) because if human life has a value and if you find out that this is a fact ( which would make the opposite claim wrong and maybe fallacious ) you would have knocked out an entire field of philosophy on which brilliant mind have been struggling for years.

If you believe I'm wrong, then I would demand you to develop on where the fallacy is here, because in the end i steuggle to see any, i just see a philosophical and ethical ungoing debate (And it's rare to see a philosophical question solved by a final yes or no answer, it happens sometimes but it's rare).

Edit : I hear you saying that reducing uncertainty is a form of measurment, but for something to be a fallacy it needs to be fallacious regardless of anything, if you can bring a valid argument in favor of this claim in a different way it's not a fallacious argument, just a argument which can be discussed. A fallacy is always wrong regardless of how you see it " Vaccines cause cancer because my son got cancer after his shot " is a fallacy and is wrong regardeless of everything.

" We cannot put value on a human life " is not a fallacy because a valid argument could be raised to support the claim, the best you can do is saying "How lazy of you ! Let's put some value on it and see if we fail so much that i'll have to admit you're right. And if we succeed, then pay me a beer"

Good day to you

Fallacies are about ways of reasoning and not the results of it. What you are talking about here is more a result of reasoning that might be right or wrong.

While as Douglas W. Hubbard shows that you can always make up a measurement he doesn't demostrate quantitatively that people who follow the heuristics he advocates as actually making decisions that lead to higher utility then people who don't follow his heuristics of measuring everything. His argument is completely qualitative in nature. This should make the reader a bit suspicious ;)

You also haven't quantified a single variable in your post.

Its possible that he's right. It's also possible that if people would do what he advises they would Goodhart on metrics that lead them to make worse decisions.

On the subject of the value of a human life, Agnes Callard's interview with Tyler Cohen is quite insightful. In it Tyler brings up how economist think they need to put a number on the value of a human life to make decisions about which safety regulations should be passed and Agnes shows quite easily how that's false and likely duo to economists simply being ignorant of the underlying philosophical matter.