According to recent research it actually appears that humanity was way more social and peaceful (way) before there were real (written) laws. Maybe one should have a look at small tribes that are completely untouched by the so called civilized world.
My personal guess (and really just a guess) is that numerous bad sociological events (see the middle ages) caused society to not be able to respond to it in a good way, because everyone remembers how something went really wrong. Therefor everyone things laws are important, which seems to be wrong, if you take a look on how unwritten laws that in a way are enforced by society (giving certain reactions) are way more closely followed.
Or just things where as a child you hear "No, don't do that".
A lot of cruel things are not, should not and can not be enforced by laws anyway.
One could also think about social animals (that still are more individual than ants for example), like elephants, which when it comes to social structures and also dealing with death, etc. are actually really close to the humans (choose another animals if you want) that usually are kinda peaceful and social when dealing with others of the same species. Same for apes and stuff of course. So, since they are doing so well and humans seem to (genetically) be more social I doubt that the lack of hard punishments really cause problems. Punishment in these cases does not mean to be killed, being robbed of all your belongings or be caged for many years of your life. So I actually doubt that it can change so much more for humans.