Make Players Choose To Be Kind

One big advantage to an assumed amoral style of play/setting that not many people talk about is how it forces players to actively have to be kind. 

In other play styles (notably WotC "heroic fantasy") the "goodness" of the heroes is usually treated as default. The players and their actions are "good" because they are the "heroes" and this is part of the reason that such extreme murderhobo behavior can be found in such settings. When players just are the "heroes" not dependent of their actions it can create a disconnect to the reality. 

This often is further worsened by NPCs just ignoring players actual behavior and other railroading problems. It makes players want to have an impact on the world so they start going to extremes, classic murderhobo behavior. 

So instead assume amorality. Treat players and NPCs like their people. Complicated and ultimately ever changing. If players are to do good then they must actual actively do good. 

When good deeds arise naturally out of the players choices, especially when players rejected other options that were more beneficial to them, it is immensely satisfying. Far more than if players are just assumed to be heroic by default. It gives agency and meaning to player choice.

It also teaches and reinforces that fact that kindness is something that takes effort which can be an important moral when playing with younger players.

An important thing to remember when putting this to practice, though, is that even if being unkind, cruel, or selfish would net the players more benefits they should still get rewards from the kind option. Just adjust accordingly. Save the thief's life? Brand new best friend. 

Rewards for kindness should be in the relationships the players build within the world.

I think ultimately the key advantage to this is just that it is so much more satisfying for players to decide to be the heroes.