The decision that MC made was morally and ethically correct. I also think it was the right choose. Other people also complained "that 'girl' will whine", which will most likely be the case. However, even if the MC resurrected his 'step mother', do you think she won't be whining him to "not kill human" as well. So, either way, it will go down that "don't kill human" path. I personally don't think a plot where MC going a on "human extinction" mission would be pleasing to read (although I did enjoy his destruction on humanity early), at least in the long run.
So far, I'm enjoying the art and the plot. So keep up the good work dear author and translator(s).