>>adrian+R3
What is just is decided both by an individual and the society they exist in. "It is one's moral obligation to fight injustice" is a pretty common tenent to hold. Injustice can be city laws encouraging anti-homeless spikes. Injustice can also be genocide in a remote country. Those injustices get fought in
very different ways. One can be handled by individual vigilanteeism and peacefully petitioning local governance. The other might require global war.
In my personal belief, everyone[0] has the right and moral obligation to fight the injustice they care about at the level they can manage. If that's handing out water at the protest or inventing penicillin, do what you personally can do to improve the world.
[0]the average layperson, obvious exceptions for power/money apply