I think it's very relevant. We're discussing western morals and good/evil here, because those are at the root of the alignment system and the common usage of good/evil is what 5e uses.
Every one of the legislators was born and raised on those morals and those morals come out in the laws. Using lethal force against non-lethal force is illegal, BECAUSE it's evil.
I disagree. The role of a government is not to dictate what is good and evil, but rather to create rules that allow for a functional society. When governments hold themselves up to be moral authorities it's generally time to be wary IMO, because such governments quickly become oppressive from what I've seen.
The problem stems from the fact that two ideas of what is moral won't necessarily the same. We can generally agree on the major points (murder is wrong), but there are many other points where people won't agree. To avoid any real-world examples, let's imagine that in some fictional religion it is taboo to wear the color blue on alternate Tuesdays. To devout followers of this religion, wearing blue on those days is a grave sin and might even be considered evil. To non-followers, there's obviously nothing wrong with it. Arguably, society is not hindered from operating smoothly if some people wear blue on alternate Tuesdays. As such, if followers of this imaginary religion were to push through a law prohibiting everyone from wearing blue on alternate Tuesdays, I would consider that oppressive and evil even though many followers of that religion would likely consider it to be just and good (and I guarantee you I would still think that way even if I were a follower of this fictional religion).
That isn't to say that legislation which is in line with the tenants religion is bad by default. Sometimes the rules which governments create dovetail nicely with morality (you can't go around hurting people just because you feel like it is a good rule both for an orderly society and a moral one). Other times those rules have little to nothing to do with morality (I don't think too many people would argue that parking in a no-parking zone is an evil act, but it will still get you a ticket).
I think it's not only a mistake but also outright dangerous to conflate the two. It is not the government's role to dictate what is moral. In trying to do so, governments create less moral societies. Morality is heavily about intent IMO, therefore if the only reason I avoid wearing blue on alternate Tuesdays is to avoid the legal ramifications, then I'm not being moral even though it might appear that I am.
Using lethal force against non-lethal force is illegal because it is bad for a society if every time someone throws a punch, the other guy pulls a gun. If that sort of thing were allowed you'd soon have anarchy. Keep in mind that from a legal perspective, even using non-lethal force is prohibited for most people under most circumstances.