Dinesh D'Souza asked John Loftus in their recent debate something to the effect of "Why bother debunking a being that from your perspective is mythical? You don't see me spending so much energy trying to disprove the existence of unicorns."
Here's one reason. Christian belief could contribute to the end of the human experiment. I know that sounds extreme, but consider.
Assuming you are not a Christian, what things do you think are most likely to lead to the extinction of humanity? Well, one would probably be what Albert Einstein and Bertrand Russell raised in their Russell-Einstein Manifesto. They wrote:
Here, then, is the problem which we present to you, stark and dreadful and inescapable: Shall we put an end to the human race; or shall mankind renounce war?
Obviously mankind has not renounced war. This threat remains and it is substantial.
Another way is environmental catastrophe. Drastic environmental changes are frequently the cause of the major extinction events throughout the history of life on this planet. During the last half a billion years there have been 5 extinction events that have caused over half of the animal population to die. The consensus of climate experts is that humans are causing changes in our climate that could lead to catastrophic results. See here for a brief primer and go here for the IPCC reporting. It's not a guarantee, but it is a risk.
So what can be done to reduce the risks? On the nuclear front I think it would be great if the worlds leading power stopped threatening and attacking various countries. This can lead to further nuclear proliferation amongst fundamentalist extremist Muslim nations, as I discussed here. On the climate front we probably need to reduce our carbon emissions.
Here's the scary thing. Evangelical Christians don't care. I know because I was one. I didn't care. I also talk to evangelicals today. Most people I know are evangelicals. They don't care. Want to know why? Jesus is coming again. Why should I reduce carbon emissions? Why should I be concerned about nuclear proliferation? Is Jesus going to let that happen?
The fact is this is a rational position from their perspective. Evangelicals are a disproportionately high segment of global warming deniers (see my earlier discussion here). They are also a disproportionately high segment of war advocates against extremist Muslim nations. They are doing things that increase the likelihood of nuclear proliferation and global warming and so they are doing things that increase the likelihood of the extinction of humanity.
Since deconverting I've realized some things. There's no God that's going to clean up our messes. We destroy our environment and we are on our own. We will face the consequences. No magic man will wave his wand and make it all better. God is not protecting us from enraged Muslims smuggling nuclear weapons into our country. If we don't take responsibility and do what is necessary to reduce these risks then we could destroy ourselves. It took deconversion for me to realize this.