One of the base principals of any species is to procreate. “Be fruitful and multiply” Genesis 1:28. This value is ingrained in every species, and rightly so, because without it the species does not continue. The opposite of this tenet is to indiscriminately kill: We call this genocide. Genocide is the indiscriminate killing of a group, regardless of who they are, what they have done, how old they are, to kill because they are a member of a species. When Russia invaded Ukraine and proceeded to launch missiles to indiscriminately destroy civilian and military targets, lots of people died. This is genocide.
I am Canadian, so cannot help but be sympathetic to a Canadian viewpoint. This sympathy unconsciously biases my views and I do not apologize for this as it is normal. When I ask if a country has the right to kill its own citizens, I am specifically asking whether it is morally right for China or Russia to discipline and kill its own citizens.
In the Western context, which I am from, there have been recent cases where citizens have gone abroad to join foreign armies and have vowed to return home and kill their own citizens. In these cases the US and Britain have allowed their forces to kill their own citizens, citing self-defence and national security