How is this even up for speculation?
  Why is there a need to quantify this with a study?

Legislation and governance is influenced by statistics. If a City Hall meeting is discussing legislating against Uber, and a taxi commission presents a paper demonstrating that Uber will cost $X in economic loss to the commission, it behooves Uber to present a competing analysis: showing $Y savings relating to drunk driving (or whatever else they can show).

On the face of it, it seems sad that everything - even the cost of human life - is quantified.

But it is a rational argument when making trade-offs:

"This new pill is better than aspirin." "OK, let's use that instead of aspirin."

Vs

"This new pill is 0.1% better than aspirin." "How much does it cost?" "Ten times the price of aspirin." "OK, so the effect is 0.1% better, but we can only treat a tenth of the number of patients? Better stick with aspirin."

Seriously. No shit it helps.