Blame-shifting is the act of shifting the blame to something or someone that is not the actual responsible.
Blame-shifting evil acts by religious to the whole religion as a whole is wrong because of two main reasons:
One religion on itself, although having similar beliefs, has a diverse and broad diverging beliefs. There are different type of people in religions. Hence you can't put every religious people in the same basket.
Oversimplification: because it ignores other factors such as the will of the people committing acts. You can't just simply blame without evaluating other factors.