Most of us know good people who are religious and we know some good things have been done in the name of religion. Indeed Canada would not have Medicare, public pensions or most of it's social programs if it was not for CCFers and New Democrats inspired by the Social Gospel.
However we also know that any rational understanding of history finds that way more evil than good has been done in the name of religion that and religion is the tool invariably used to get good people to do evil things because "god is on our side".
It is not any specific religious doctrine or act in the name of "god" that is the most harmful thing about religion. Rather it is the religious mindset. It is the religious mindset that allows people to reject facts and reason. It is the religious mindset that allows people to believe something just because they choose to, or because someone like Osama Bin Laden, Adolf Hitler or Glenn Beck tells them to. It is faith, belief with no rational basis, that is the foundation of all religion and which makes it so dangerous.