Four reasons : to pocket honoraria, to sell books, to draw blood, to impress their fans. It does not even occur to them that they might change their opponents’ opinion, any more than that such debate will change their own. They love scoring points, they relish the applause, they thrive on the repartee. Although they can predict the topics debated, they have to be on the qui-vive for the curve-ball, which they welcome because nothing pleases the audience more. Such debates are essentially entertainment, and perhaps even worth the entrance fee. And at home they sure beat the other garbage on the tube.
The rest of us should resist the temptation to waste our time trying to change the mind of confirmed atheists or confirmed believers, an exercise which is even more pointless than public debates between celebrities. At least the latter serve one useful purpose : to provide Believers on the Brink in the audience with arguments, insights and information to help them decide whether they should let go of their remaining beliefs or, on the contrary, dismiss their doubts and reaffirm their faith.
You now know why I have given up arguing with confirmed non-atheists about reasons for and against belief in God’s existence, the claims of divine revelation and the myth of the after-life. I prefer to devote my time to Believers on the Brink, to help them examine the reasons for their doubts and for their hesitation to “let go”. Only people open to question can be influenced to change their mind. I am not about to change my mind, any more than my non-atheist friends are. Both of us would do well to avoid talking to brick walls and devote our energy and conviction to convincing the undecided.