What purpose of government would have the most dramatic effect on society if it were taken away answers?

I don't know what your options were, but let's think about what's the worst that can happen to a human?

Death.

Is one of the purposes of the government to prevent death?

Yes: national defense and control of epidemics.

So I would argue that national defense (protecting the citizens from being attacked by others) and controlling disasters such as epidemics are the two purposes of the government that would be missed most.