Trying to get believers to re-examine their religion is a difficult thing to do. You have to be just subtle enough and just friendly enough so that you don't leave them feeling insulted and angry. But, you can't be so subtle and friendly that they actually think they "won" the argument.
Usually you want to throw barbs, not hand grenades. Barbs that get stuck in their thoughts, pricking them, bothering them until they give the point more thought. You can't expect to ever win. They will probably never de-convert right before your eyes
Sometimes you just have to realize that you are trying to change something that you can not. There actually are people so lacking of capacity for independent thought that precipitously depriving them of their delusions could be harmful to them--or to you.
When someone believes in something that is patently false, it is because he has an emotional need to believe it and trying to dissuade him will only arouse a dangerous emotional reaction. You are threatening to force him to face something that he simply cannot face.
With regard to religion, I think the threat is most often to the believer's ego. Religion is a huge part of the believer's self-image and his social status. Getting someone to face the fact that he is wrong about something so important as his entire worldview would be tantamount to getting him to face the fact that he is an utter fool. He will likely become enraged.
In cases where believers actually face the reality of the way they have been duped, they often become enraged at those who played them for fools. Believers usually, however, will not take that step--and that step has to come from within, you can't force it on them. If you try, and I have, if you corner them with logic they will usually become enraged at you. This video clip presents a classic example. Many of them, in fact, are always enraged at atheists for this very reason. They know what we represent. We represent the viewpoint that they are fools.
I have found that this particular rage is extremely dangerous. Especially when dealing with "intellectual" believers who are vain about their mental capacities. Usually this vanity is abnormally large and is extremely important to their self-image. Usually, it is nothing less than pathological narcissism. I know this because I know that when you corner them with logic, they engage in a primitive psychological defense mechanism known as "splitting", meaning splitting the world into absolutes, "good' and "evil". They will see you as being completely evil from that point on. Everything you do and say will be seen as evil and will be twisted to support this view. An example of this is Chris Hedges' reaction to being bested in debates by Sam Harris and, particularly, Christopher Hitchens. I respect and admire Chris Hedges as much as any person on this Earth, but he is still a believer and still only human.
I gather, too, from my experiences with older religious "intellectuals" that most of them have indeed been cornered with logic at some point in the past and chose to engage in "splitting" rather than face what logic told them. As soon as they are sure you are an atheist and not an agnostic, they will see you as just as evil as the one who cornered them in the past. This puts you in more danger than you know. They won't assault you physically, but they will thenceforth nurture an undying hatred for you and do everything in their power to disrupt and damage your life.
People are at their most dangerous when they are not thinking rationally and when their egos are threatened. Trying to argue a believer out of his religion causes both of these conditions to occur simultaneously. Always protect yourself and always remain emotionally aloof. Never let your ego become too involved and never threaten theirs too directly. Plant your barbs and walk away.