"Why don't you argue against UFO believers?"
The answer is quite simple. People are not trying to get belief in UFOs enshrined into national law. People are trying to legislate christianity. I also don't see con men trying to use UFO belief to market their scams. Yes, I do see spoof merchandise. But the primary market for that is the set of people who laugh at UFO believers. I consider christianity dangerous because too many people want to use it to interfere with how I live my life.