Many of us think that tremendous growth in the number of people on earth is dangerous. It has exacerbated climate change as well as international tensions. There is no clearly ethical way to reduce population growth, let alone eliminate it.
Therefore we could be grateful to all the people who refuse vaccinations. They are volunteering to risk death and infecting others. They use their freedom to be open to illness in a way that might make the rest of us safer in a less crowded world.
They usually do not know what they are doing in this regard. They might know that previous ages have had much lower life expectancy and affirm that that is good. Old age full of infirmity and pain is not worth it. Better to die earlier and save oneself and others from nursing homes.
Wars used to decrease population and they still work a bit, but there are not enough to do the whole job. Modern warfare is supposed to avoid killing civilians. It is cheaper to starve them and weather problems help. Terrorist attacks and raids are sad but not big or frequent unless planes and atomic bombs are used strategically.
Preventing vaccination of enemies can help the spread of disease among them and the rest of the world, encouraging new deadly virus variations. Simple neglect of sending vaccines to other countries does the same without antagonism. But businesses might have fewer places where cheap labor can be found.