Memes

In my opinion, the main purpose behind law and punishment is deterrence from immoral actions.

There's an element of that. Also, the idea that certain people need to be separated from general society as a precautionary measure. But I think there's also a broad concept of social justice. 2nd degree murder is a good example. Nobody really expects murder charges to prevent people from going into a killing rage. And there's no way to undo the damage inflicted. So punishment is intended as a kind of social vengeance, intended both to shame the perpetrator and to alleviate the desire of the victims to pursue their own vigilante justice.

I think simply achieving material flourishing isn’t enough to make people moral, mainly because there are other instincts at play.

I wouldn't say it is sufficient, but I would say it is necessary. A great deal of crime is the consequence of anxiety, in one form or another. Relieving the anxiety reduces instances of crime.

Sure, there are other instincts at work. But defusing these tensions will also require infrastructure, energy, and manpower. And so you can establish a virtuous cycle, wherein a professional class of social workers with the means and methods to deliver aid also become a vehicle of economic activity that reduces poverty and contributes to the benefit of the community.