Is it just me or...
The mc being too scared to kill something a really common trope in Isekai now?
From what I understand - this is normal for humans. If the MC is an accomplished warrior from a fantasy world, he has already came to terms with killing long ago.
But for a guy who was suddenly thrust into adventure (whether a fantasy kid or a otherworlder from a peaceful world) killing people is not easy. And that's the way it should be, otherwise we humans would have all killed each other long ago.
And so, first killing of a person is always a milestone for a realistic character. In fantasy, it is possible to have multiple of them - first animal-like monsters, next monstrous humanoids like goblins, next human-equivalent beings of other races, and finally enemies from one's own race.
On the contrary, not having problems with one's first killing is a bad sign that you might have lost your humanity somewhere. Probably normal for people reincarnated into weapons or giant spiders. But if you're summoned and have no problems with killing, you should probably look into whether you should kill the faction that summoned you, because they have hidden mind control spells in the summoning.