I can't speak for anyone but myself, but I can tell you why I do it, and why I constantly challenge religious belief and religious explanations of everything. In all of human history we have found only one method for reliably establishing the truth content of ideas, and that is the method of science. It's about logic and evidence: how does nature actually behave when probed? That experimental attitude is responsible for much of the quality of our lives, and it's only about 400 years old. The medical science that prolongs our lives, the technological gadgets like this computer that inform and entertain us, even something as mundane as the clean fresh water that comes out of our household taps and the sewage systems that safely carry away our wastes, are products of science. Science and the technologies it fosters have improved our lives immeasurably; they work, and they work consistently and reliably. A smallpox vaccination will protect you indefinitely against a horrible disease that once killed millions, and it works whether you believe in it or not. No religion can make a claim like that.For those who have definite opinions - religious or otherwise - why is it we feel the need to prove it to others what we believe.
I am a committed and unapologetic admirer of science and technology. It is demonstrably the best way we've ever found for understanding the world we live in, and in my view, if you reject its precepts, you are simply wrong. Analyses and understandings that are not based on reason and evidence and the methods of science have no credibility with me, and religious belief is at the top of the list of things I reject as irrational, unfounded, and undemonstrable. 10,000 years of religious belief has made no contribution to the quality of our lives anywhere close to what science and technology have done for us. It wasn't very long ago, only a generation or two, that parents could routinely expect most of their children to die of infections before they were 10 years old. That hardly ever happens anymore, at least in what's called the developed world, and science is the reason why.
Irrationality doesn't go anywhere, it's just wrong. That's why I constantly challenge religious beliefs and religiously-based understandings of the way things are. They are fundamentally irrational, based on belief in the absence of evidence, and often in the face of the evidence, and that's not a good way to understand things or solve problems.