Ok here is the scenario.
It is 20 years in the future. It is 9 years after humanity has engaged in global biological / germ warfare with devastating results. State sponsored terrorism and the use of bio / chem weapons resulted in a third world war. No nuclear weapons were used. The weapons used made the human species exceptionally susceptible to disease and illness that we previously had strong immunities to. Women were rendered infertile and children were the most vulnerable and had the highest rate of mortality.
The human population globally has been reduced to 30,000. There are no functioning governments, civilization has broken down. It was never understood why a small percentage of the species seemed to have some resistance before those studying the problem died out. That vast majority of the remaining survivors are the disorganized remnants of former violent gangs. In the US these include groups such as Crips, Bloods and MS13, in Africa these groups are tribes such as the Huttu and Tutsi. In every part of the world, the only large population centers (which never exceed more than a few thousand) are exclusively savage, powerful and barbaric former gangs that operate on a tribal level.
They control the remaining large weapon arsenals, warehouses of food and medicine and whatever constitutes wealth. The rest of humanity, which exist in much smaller population groups (usually no more than two dozen) live in fear of the larger gangs and avoid them and the population centers they reside in at all cost. Their numbers in the last few years have been dramatically reduced by the larger gangs and they now represent about 2% of the surviving human population. The larger gangs hunt them with the goal of completely eradicating them so that they will be all that remains.
The human wanderers who are not simply murdered are kidnapped and forced into slavery. Females are kept as sex slaves and raped. Males used as expendable labor. Those who possess threatening traits such as intelligence, strength, organizational or leadership skills are executed immediately. The dominant gangs tolerate no challenge to their authority and will not permit the survival of anyone they don't control. Constant inter gang rivalry and warfare prevent any additional organization and continue to reduce the human population.
You are one of the human wanderers, trying to survive the every day struggle for food, shelter and avoiding predators. You have no surviving family members and only occasionally come into contact with small bands of humans such as yourself. While searching for supplies you come across a medical center that had successfully developed vaccines that were never distributed. You hold in your hands the key to save the human race.
There is just one problem.
The only population centers large enough to sustain the species are the large gangs. The vaccines (which will allow females to become pregnant) would not realistically have the necessary success rate on small bands of a dozen or so humans. More importantly, these fertile females and their children would most likely fall into the hands of the violent gangs and be used to breed their offspring. So while most people would prefer to build up the less violent remnants of humanity and have them reproduce the future of the species, that really isn't a viable option and they are already at great risk of becoming extinct.
So to rescue the human species, you would have to supply the vaccine to the larger, violent gangs. They would become the future of humanity. And to add insult to injury they would most likely kill you as soon as they no longer needed you if you did provide the vaccine to them.
So there is the ethical dilemma.
Now it is true that our modern present civilization began in many cases thousands of years ago with it's roots in savage and barbaric societies that preyed on the innocent and we evolved into something very different. But if our "humanity" becomes lost, do we really deserve a second chance? And do the innocents deserve another millennium of growing pains as we struggle towards civilization and enlightenment. And is there even any guarantee we will do it again. The societies based on the foundations of MS13, crips and tutsi might simply be endless generations of savage barbarity.
So what would you do if you held the future of the species in your hands?