How can it be just if if the market can be put in a state of unfairness?

How can people "vote with their feet" when they have no resources and are dying?

How can you be sure that the monopolist wouldn't only exploit the resources, leave the land dry and dead, then leave to another place to do the same thing, without leaving anything just and fair behind?

So, someone finds a way to provide water lower costs at the region, why wouldnt the monopolist just buy all this new water supply than what people could afford on the market for a higher price only to avoid other product than his to reach the market?

How is letting someone die more just than creating a mechanism that allow people to survive?

All the arguments i hear so far about libertarianism seems that creating unjust and unfair situations doesnt matter as long as everyone can do whatever the hell they want.