Christians celebrate rape, torture, slavery and genocide.

[Kirbmarc]

usually believe that it's a net evil, despite not being able to quantify it.

Religion is a net evil not because religious people are worse than non-religious ones (they aren't), but because the groundless arguments of religion can justify evil deeds in the name of an allegedly good purpose.

"Good" (empathic and morally sound) people are going to be good regardless of their religious opinion. The same is true for "evil" (sociopathic and morally unsound) people. The only difference that religion makes is that it drives good people to commit evil deeds for unproven good ends.

Of course this true for many other ideological constructs, such as communism or fascism, so all the philosophical concepts that promote a "the end justifies the means" attitude are a net evil.