He led an enterprise with the goal and the result of making a bit more money by ending and ruining numerous lives.

He led an enterprise with the goal of making money by offering healthcare insurance. Unless you’re a mind reader, then your assumption that he wanted it to be earned specifically by ending and ruining lives is conjecture.

the money guy says “nope I don’t think you need that, denied”

“I don’t think you need that” is not a valid reason for rejecting a claim. They cannot simply say no without providing a reason.

they are actively doing harm to numerous people for a small monetary return

How does that work? Where does this return come from?

They get a pretty bad punishment because their actions can directly be proven to have caused an innocent death. And it may have been predictable, but it wasn’t intentional.

Who doles out this punishment?

Brian Thompson set policies that caused many orders of magnitude more death and suffering

What policies are those? Be specific.

However, having “the law” on his side, there were legal and corporate structures in place to insulate his decisions

Which decisions are those and what laws helped insulate them. Be specific.

I used to think more like you. Surely since the rule of law is the ideal, we should choose that side of any argument like this.

I do not think the rule of law is ideal. I think there are tons of laws on the books that are immoral. I also notice the killer didn’t target any of these lawmakers.

I also don’t care about Brian Thompson as a person, I don’t care that he’s dead either.

In fact, I think it’s possible to have a situation where vigilante justice is morally justified.

This is not one of those cases.