I've completed an almost pacifist run on Dominating, and I even have saves left. And fully pacifist run is also possible. What is not possible is no kills run, and no combat run. Definition is key. I will make an entire post about this run in general sometime later.
To be short:
1)My rule for this run was: "My actions should not cause harm and unnecessary deaths if possible". That is how I defined pacifist run.
2)There are 2 things you are absolutely must kill in order to finish the main story - Pulsating roots and Tchort.
3)Robots, any critters, animals, etc. are okay to kill if necessary.
THEORETICALLY, even 3) can be avoided with one single exception.
Now, for the "almost" part:
In this run I did not kill a single mutie or mutant, however I did caused deaths of 3 humans if I remember correctly (Jack's first quest, I accidentally exploded a barrel near rathounds with electrokinesis, and the sound attracted thugs, and then rathounds killed them). I killed a few stalkers in Arke Basement (I think it's avoidable), some robots and psi-beetles. Spiders in a lab near Foundry. Possibly some rathounds, dogs and mutant dogs, I don't remember.
There is a lot of BS in your post, like
"You can't kill dogs, they are humans too"
"psi beetles also humans, wish you or not"
"you can't kill rathounds. They are humans too. You can't kill robots, they are humans too"
and especially
"But all games teach something, in this case kill innocent people"
I'm not going to reply to all this, I'll just say it's wrong. Also Tchort is not a human(s). It was once, but not anymore.
Returning to the topic of this thread -
>It is RPG!
Exactly. Clearly Phreak needs this shit, or else he would sell it to you or give it as award for doing his quests. You either kill him and get the glove, or you don't kill him because he did nothing wrong to you, but in that case you won't get the glove. A rather basic example of choice as far as RPGs go, but still. If you remove the choice, RPG part of the game will be gone, and it's already not a strong part of Underrail in my opinion. And finally, it's not a big deal to miss this item.
Someone have completed pacifist run on youtube, I think it was Tygrende; he used Enrage on tentacles to get the boss.
In my run, I used Temporal Manipulation and Psychokinesis.