I am not so keen on the US system, even though I have lived in it. I know some higher judges are definitely political appointees, perhaps the lower ones have other ways of being chosen.
Manslaughter and murder are different things, because the law has defined them as such. This is the law trying to make its flexibility concrete.
I always tend to think about my experience with coding a computer or a website. There are always situations that you cannot anticipate when writing the code, thus there occur bugs, exploits, hacks, etc.
Then we must return to the code and adjust, add flexibility or change entirely.
The law is the same, except we are imperfect unique beings! We need much more flexibility that even computer code can express.
Thank you for such an interesting discussion.