Dylan Galos isn't saying anything against religion. He's simply saying that he's an atheist and a moral person. The only thing that can really be offensive about this is that he's an atheist. That's it. The fact that atheists exist offends people.
In the U.S. I suspect it has a lot to do with the Cold War and the "Red Menace". The Communists were officially atheist and they actively suppressed religious freedoms. I guess that people came to conflate atheism and Communism. It probably all falls back to a more general human behavior regarding people with different ideas. You can see the same thing happening now with Islam: "The people we feel threatened by are Muslim, therefor Muslims are our enemies."
On the other hand, some people seem to simply be threatened by people who disagree with them. The Evangelicals I grew up around were just as offended by Buddhists and Hindus as by atheists. I've even come across people who actually took offense because I didn't care for a particular band or style of music. I made it clear that I was not claiming that there was something inherently inferior about said music and that I didn't think anyone was wrong to like it, but I was still treated as though I'd made a personal attack.
I believe the people offended by atheism are people whose faith is the "blind" variety. They make no effort to think about their belief, and may secretly harbor doubts about their faith and worry that they may be wrong. Their failure to analyze their beliefs gives them no rational basis for their faith. Their sense of who they are is based on their faith, and the thought of it being unfounded is as disconcerting to them as if they were finding out they aren't actually human but the result of a lab experiment in genetic manipulation in cats.
Those believers who have examined their faith, who have doubts about aspects of conventional religion and who recognize that there are valid arguments against their belief, tend to be unafraid of and un-offended by atheism and atheists. I believe this is because they have a handle on the foundation of their faith, have examined and understand most or all of the big questions and have reached a conclusion that seems right to them. Many atheists went through a similar rational process and reached a different conclusion.