There is an interesting article here that is worth reading. It's flamingly pro-life and I don't agree with some of the article, but the primary point the article makes in terms of debate and dialog whether religious, theological, political, or what have you is worth considering. What he is discussing, though does not name, is the rhetorical idea of the non sequitur. That is basically Latin for "it does not (necessarily) follow..." In common parlance, one might say a debate that uses this involves comparing apples and oranges.
You saw this last night several times in the Presidential debates. The question from the moderator would involve something having to do with some domestic policy issue. Each candidate would then say something like, "You should vote for me because my opponent believes Y (about this policy involving X with which nothing to do with Y." While is might be true that the opposite candidate might believe Y, that is an illogical position in relationship to the question posed about X if Y has nothing to do with X. That's just a cheap shot non sequitur argument.
But why do people make non sequitur arguments? Going all the way back to Cicero's rules of rhetoric, you make non sequitur arguments that are not on point to distract the listeners from the fact that your own position on the substantive issue is not convincing. Non sequitur arguments attempt to tap in to the emotive centers of the brain because emotions are not rational and, again according to Cicero, emotive appeals mask the fact that the orator is failing to logically appeal to the brain or intellect of the listener. In other words, emotive appeals are what you throw out when you have nothing else in your rhetorical arsenal. You hope that by playing on emotions, you can fool the audience into not critically evaluating your argument on its own logical merit.
In an incredibly emotive society, this is a very effective ploy. This is true also in the realm of moral or theological debates. One of my utter frustrations with the ongoing "dialogues" about sexuality and marriage and all that is the fact that people who do not hold my opinions have failed (utterly in my opinion) to make a rational argument in favor of their positions that I find convincing. They seem to have no qualms about throwing out what the Bible or Holy Tradition (or even reason for that matter) has to say on the topics in lieu of making arguments that are completely emotive based.
Classic example: "If you just get to know gay people, then you wouldn't believe what you believe on homosexuality." This is a perfect example of a non sequitur argument. I know a lot of gay people; I have gay friends; I know many of them are fine upstanding citizens. That has no bearing on whether God smiles on homosexuality or not. I get the same non sequitur argumentation from people who scoff at my hesitation about cohabitating couples living together before marriage. "Well, everybody does it now," they say. Again, fine people who might very well mean well and be fine upstanding citizens. This has no bearing on whether it is right or wrong. Everyone sins. This is not a new revelation. The question is, "Does this behavior separate us from God's plan and design (i.e. is it sin)?" Whether they are nice people you'd be happy to have afternoon tea with or not does not speak to that question.
Now, let me be clear: I would love nothing more than for Jesus to walk into my office as I type this and tell me I have it all wrong on these issues. It would make my life in the Episcopal church a whole lot easier. Jesus does not tend to make personalized house calls too much these days, so I have to exist and try to figure things out with the logical mind God gave me.
If I am talking about X social problem, it is not logical for the person with whom I am conversing to drag in Y social problem (or some other topic), when X and Y do not have anything to do with one another. That's the guts of it. Until both sides of whatever argument can agree to stay on topic and speak to the question itself in a logical manner and not attempt to compare apples and oranges, no real progress will ever be made on any substantive debate or policy.