Let me elaborate on my initial response:

Goblin Slayer is just a marginally sanitized Day of the Rope fantasy and identifying with it is school shooter shit.

Light's case is more complicated but not very much better, though Death Note is much better because it expresses clearly from the outset that Light is not a good dude. Of course, the authors behind it are stupid, narcissistic pricks, so they don't understand the full magnitude of what is wrong with Light because they import their own pathologies when making their "relatable villain," but they did at least intend him to be mainly villainous (the psychopathic way he manipulates people who personally care about him can be taken as clear evidence of this, and the heroic light that the bulk of the Kira Task Force is painted with, especially Light's father).

What was Light's method of operation? In the overwhelming bulk of cases, he waited for crimes to be reported on the news (or went through records of past convictions) and killed people who were convicted of crimes that he deemed sufficiently heinous, mainly murder, trafficking, etc. He did not target white-collar crime, and we know this because around a quarter of the way through Kira does start targeting them and the Task Force, which knows who 99.9% of his victims have been, note it as a change in his method. This is not an enduring element and is done for extrinsic reasons.

Of course, you and I know many facts relevant to this set of premises: Most major white-collar crime is unconvicted, many black-collar convictions are false (and Japan just loves convicting). While killing someone will be liable to get you convicted of murder, scamming a hundred people out of their houses and causing one person in ten households to kill themselves and several dozen to live in squalor is probably just going to get you a fine at worst if you are part of a major bank. We also know that crime does not just happen for no reason and that the reason is often engineered (by the white-collar criminals, their colleagues, and their puppets)

So, whatever he says, what does Kira's "justice" amount to? That the existing court system is just fine in every respect except that it is not brutal enough towards those who it convicts of sufficiently lurid-sounding crimes. He has basically done nothing except re-establish the death penalty in Japan, since it is still totally dependent on court rulings even though it is carried out by someone who isn't connected to the courts. It represents nothing better than a regression to an earlier period of postwar Japan in this respect.