It can have ether effect or contribute very little. In some societies like Finland where it is estimated that 70% of the population owns a gun, they have one of the lowest crime rates in the world. Some Fins believe that because everyone is armed (although the guns are in homes), that crime is lower.
In the US however where about 40% of the households have guns, gun violence is out of control.
So it seems like the society determines greatly whether there will be lots of gun violence even when there are lots of guns in the society.
Another point is that Finland has a very homogeneous society, the country is relatively affluent and its people embrace social principals.
The US is a melting pot with many different cultures trying to co-exist, there are lots of high poverty areas and capitalism i.e. "everybody needs to get paid" prevails. You put guns into the society that is America and you get lots of gun violence. Did the guns cause that? I would have to say no but they certainly contribute to the violence meaning if there were not so many guns less gun violence would occur. this happened in Australia when they changed their gun laws. Gun violence was out of control and now it has dropped by more than 80%.
Sorry for hte long winded answer but in my opinion it is complicated. Let me summarize. Guns in some cases can be a deterrent to crime and in others they can cause more crime depending on the society. Thanks.