I would argue however that In many instances however it is the religion that is used as the justification to do things as opposed to the religion itself.
Christianity was used to justify the crusades, holocaust, slavery, native american ethnic cleansing, etc
Judaism is used to justify settlements, land reclamation, apartheid, etc
Islam is used to justify revenge, minority blaming, external influence blaming, etc
Just another tool in the toolbox for leaders to control people. Isis' commanders consist mostly of ex-Saddam military generals (Sunni) who are getting revenge on (Shia), and this is why they have had many tactical successes. They changed their names and such to religious ones of course; but their motives are entirely for power. The Pope wants to remain influential, Christopher Columbus wanted the gold, Saudi Arabia wants to blame Shia's for all their woes - its all the same.
I simply see religion's ability to influence people to do wrong as a consequence of those who control it, more so than its ability to corrupt random followers.
The worst part is that all the regional powers see it as a political opportunity to bomb anyone who isn't Isis. The Saudis bomb Yemen rebels, Turkey is bombing Kurds, and now Russia is bombing non-Isis rebels.
http://www.theatlantic.com/international/archive/2015/07/strategy-isis-defeat-board-game/400034/