Can anyone tell me why so many of our world's religions are responsible for so much macre and bloodshed

No one who is an intellectual or well informed in history, psychology, religion, will tell you that religion is a good thing. It is not. It is a failure. Something else will come along to replace it. More deaths have been attributed to religion that to disease (of course this includes religious wars, the Inquisition and so on). A person can be righteous and have love for his fellow man without being told by some Reverend or priest that this is what he should do. Furthermore, a person can believe in God without any connection to a specific church. His/her devotion to God can be honest and loving without reading books of fiction that instruct him/her what to say and when to say it. God doesn't need temples and churches for people to worship Him. A person can worship God in his/her heart without the intricate trappings of a church or temple. To conclude, anyone who knows history of the world knows how many wars were fought in the name of Christ or Allah and how many poor souls were lost because of these battles. As you said it...absolute atrocities!