Is it useful to set some incidents of mass killing apart and call them genocide?
There is, of course, no objective answer to this question. It is possible to argue it from either side.
On the “yes” side, are those who would argue that the motives for which mass killings are done make them morally different. From this point of view, it is worse to kill people out of hatred than out of a desire for power. Racial, ethnic, or religious hatred is, in this view, more dangerous to the world as a whole. It seeks to kill specific people, thus making everyone who is of that description vulnerable. It is also a more aberrant impulse than the desire for power.
On the other hand, we can argue that there really is no moral or practical reason to distinguish between types of mass killings. From this point of view, Stalin’s purges and mass killings were just as evil as the Holocaust because they, too, typically involved killing huge numbers of people for no real reason. There is, in this view, no moral difference between killing people because you want to take and keep power and killing them because you hate them racially. Both are devastating to the people involved and both are morally abhorrent.