To preface: I am not religious, but I do believe in at least one deity. I am also a rationalist.
Religion is, by definition, irrational. It's looking at the world and saying, "There must exist an unobservable, untestable phenomenon beyond what can be absolutely proven." While there is plenty of objectionable dogma in the Bible, it offers an excellent definition of faith: "Faith is being sure of what we hope for and certain of what we do not see." You can show me your dog, but if I have unshakable faith that it's a chair, then, by god, I'm going to sit on your dog. There will be insurmountable evidence, and even proof, that your dog is not a chair, but I have faith! This is also an excellent example of why I often refuse to discourse with religious people: faced with irrefutable fact that one of their precious beliefs is incorrect, they do not change their beliefs, and instead stubbornly continue believing in their faith. (That is not to say that all beliefs can be scientifically disputed. There is no way to either prove or disprove the existence of a deity.)
The problem is that most religious people refuse to admit that. They refuse to acknowledge their blinders and adamantly adhere to their beliefs even when faced with mountains of counter-evidence. A prime example is many devout Christians' refusal to believe in evolution. Evolution is an observable and testable scientific event, regardless of if it's been occurring for billions of years, or only millenia . . . but that's an argument for another thread.
All of that to reiterate: Religion Is Irrational. When you realize that you are arguing against the faith of a religious person, you must give up refuting their illogic, and exit the debate.