At what point do you listen to humanitarian organizations and the UN? Amazing that you think 24 people is a genocide but not 60,000+.
Self defense usually implies a "reasonable" use of force, what's happening there hasn't been reasonable for more than a year now.
If someone points a gun at you you can kill them, that's self defense, if you burn their entire village down, track and kill their family members 3 generations up it's not self defense anymore
This is very different from the interstate case. If a state shoots another state in the leg and runs away, the only way to establish a deterrent is to shoot back. There is no police force to do it for me. This is the main diffference between civil law and international law.
Even in international self defense there are criterion and limits