Why hasn't anyone here discussed the LGBT or terrorism angle? It's not like those parts aren't important. In fact they are probably just as important as the gun part. Or would a conversation about all three defy an easy argument?
It's hard for me to think of what can even be said. Dogma of any form, when people treat it as an unquestionable thing, and thus treat actions done in it's name as unimpeachably moral and just... when used as such, Dogma can certainly be used to make horrible things happen. Nothing about Dogma is innately horrible, but it has this weakness. Honestly, we all have this weakness to some degree; it's a facet of being Human and believing anything.
Every one of us, whatever our philosophies and experiences and opinions, must be sure that we treat our own feelings and knowledge as fallible. This goes for people who treat Science as unimpeachable as well. We can approach truth always, but we can't know it. When confronted, we have to be able to think to ourselves that we may be mistaken.
...unless you meant talking specifically about certain religious extremist groups incensing others to kill people on the basis of whom they love or what they believe. In which case, all I have to say is to respond to them with love too. Every fundamentalist I've known, underneath xenophobia or cruelty... underneath these they act fundamentally out of a fear of others, of death, and of the uncertainty of the world. To them, their faith is a community of allies, and a rock in a storm. The only way to combat dogmatic violence is to help individuals discover that, contrary to what those preaching their Dogma may say, we are not their enemies. We are all weathering the same stormy mortal world together, and as terrifying as it may seem it is also beautiful and meaningful, and that we can better face it when we stand together.