Look, if you set up a site called DEBUNKING Christianity, you are going beyond just saying your opponents are mistaken. You are saying that their position is bunk. If you call your book The Christian DELUSION, then you are saying that their position isn't just erroneous, it's delusional. You're staking out the low ground, not the high ground. You gain some passion for your own position, but you undercut any hope you might have of walking away from the dialogue on some kind of a friendly basis once it's over. And you can't be terribly surprised that people whose position you are attempting to debunk don't like what you're doing, and hit back with as harsh as tone as you yourself employ. Why should anyone like it when they are told that what they believe and dedicate their lives to is bunk, and a delusion?
I'm not saying that debunking is always bad. There are some things in this world that deserve debunking. Of course, I don't think Christianity is one of them, but if you do, it's a free country.
If you want a polite exchange of ideas, you might want to name your site "Critiquing Christianity." Of course, some people who like to be nice might try to engage you in polite dialogue, anyway. But you should be surprised by the polite responses, not the harshly polemical ones. They go with the territory you have staked out.