This is a static view that lacks context. Indeed killing others was happening very often, the more so as you wind back the time. And this is precisely what this reflection piece could use: a bit of historical perspective, a dynamic view. A bit of "systems thinking" as well. Human groups are evolving systems.
As time passes, their behavior changes. It is best illustrated by ... precisely "killing": when one looks back starting 7000 years ago at the dawn of civilization, the (relative) number of people being killed by other people (in proportion of the general population) has steadily decreased, and at significant speed, even though not in a linear manner.
We kill each other much less than 100 years ago. 100 years ago they were killing each other much less than 500 years ago and so on and so forth.
Why is it so ? Well, evolution of the species is one likely culprit. As the human species evolves, we realize that killing people is "rather bad" for the group.
Yes, Darwin has said it and it's appropriate to bring him in the discussion here: our gene pool evolves, we evolve as a species, we try to fit ever better in our environment (as we modify it).
So what does that say ? Is it good or bad to eat dogs ? Depends on how it impacts the human species - if it's bad for it, it will be in time "selected out" and will tend to disappear, as did cannibalism for instance. If it is relatively neutral, it might continue ...
What we can say with a high degree of confidence though is that "killing others" is a clear negative and will continue to decrease.