When someone uses just one of the Seven deadly sins in a argument I have trouble with it. The other gard rail to Greed is Envy. It takes two to have a conflict and when someone points out Greed I will ask is Envy the reason someone is pointing at Greed. Greed is if someone is not using the resources that they have earned in some manner. Envy is someone calling another greedy because they have earned alot of some thing without looking at the good they do. Like Gov. Romney uses his resources to help others at about 20% but some call him greedy just because he has money.I'll say no.
I will say greed does.
On a country or provincial scale Many religions want to claim more converts, the claiming of converts and converts country leads to resources as well. With land and resources come money, control and power.
Thus they end up using money and power to gain more converts and more land ,and more resources etc etc..
In my experiences on the streets one or more of sex, drugs,alcohol and or cash will be at the root of violence.
Religon may be an excuse but I think most violence boils down to sheer greed.