Religion is in some ways a force for good, but it can also be a very negative force in the world.
In one way, religion is very good for us because it tends to help instill good moral values in people. I am not saying that only religion can instill moral values, but it is certainly one force that can promote such things as justice and human rights.
On the other hand, religion can be the cause of horrific conflicts. Once again, it is not that religion is the only source of terrible conflict, but we cannot deny that things like the Thirty Years' War were caused in large part by disputes over religion.
Overall, one could argue that religion is generally good for individual people but that it can create problems when it is used as a reason for mass actions such as wars.
When we talk of religion, we think of secterian religion. Let us imagine when no prophet founded religion. Then also there was religion, religion of every individual. I personally think religion means a set of principles conceived by a man and try to run his life smoothly.
Later on, people having seen natural calamities, began to fear and thought of some supernatural power and began to impert lessons what else to do or what not to. By and large the sages or prophets propounded their philosophy and people believed on them and began to practice it.
Religion is a force for good in the world, if the teachings of it are obeyed. Then everthing will be good but not in pretending. In Hinduism, Brahmins oppressed others in the name of religion and religion was made a professsion for them to earn money, power and fame. As a result Buddhism came into being. In the same way in Christianity also people became fade up with the church and its atrocities and now most people have begun to believe in Atheism.
Thus religion is a force for good if the teachings are scientifically explained to the mases and reiterated them to obey for the good of the world. But it is harmful if imposed on others by a group and motivate and incite people in the name of secterian religion.
Here is part 1 of a fantastically interesting and intellectual debate called, "Is The Church A Force For Good?" It will answer a lot of your questions...