tl;dr: It is worthwhile to convince people that they already, by their own lights, have reasons to believe true things, as this is faster, easier, nicer, and more effective than helping them create from scratch reasons to believe those things.
This is not part of the problem-solving sequence. I do plan to finish that, but the last post is eluding me.
Related: Whatever it is I was thinking of here (let me know if you can dig up what it was).
Today, while waiting for a bus, I heard the two girls sitting on the bench next to mine talking about organ donation. One said that she was thinking of ceasing to be an organ donor, because she'd heard that doctors don't try as hard to save donors in hopes of using their organs to save other lives.
My bus was approaching. I didn't know the girl and could hardly follow up later with an arsenal of ironclad counterarguments. There was no time, and probably no receptivity, to engage in a lengthy discussion of why this medical behavior wouldn't happen. No chance to fire up my computer, try to get on the nearest wireless, and pull up empirical stats that say it doesn't happen.
So I chuckled and interjected, at a convenient gap in her ramble, "That's why you carry a blood donor card, too, so they think if you stay alive they'll keep getting blood from you!"
Some far-off potential tragic crisis averted? Maybe. She looked thoughtful, nodded, said that she did have a blood donor card, and that my suggestion made sense. I boarded my bus and it carried me away. I hope she's never hit by a cement truck. I hope that if she is hit by a cement truck, a stupid rumor she heard once doesn't turn it into as complete a waste as it would have to be without the wonders of organ transplant.
And even maintaining those twin hopes and feeling I'd done something to improve their conjoined chance of realization, I began to feel like perhaps I'd done wrong. I could conjure up a defense - hey, I laughed first, and I'd used the exact same words before as a mere joke (with people better-informed than this who I'd expected to get it on their own). It's not strictly my fault that she didn't take it as a joke too. And hey, I would have gone ahead and had the whole knock-down drag-out argument with her if there had only been time, if I could only have had her ear for long enough to spit out more than a soundbite, if only she hadn't been a complete stranger I'll never see again.
But even without time and social pressure preventing you from having a great long knock-down drag-out argument, it can be devastatingly ineffectual to present the reasons you think are the right ones to believe some proposition P or take some action A. And presenting other reasons seems dishonest, somehow - just lining up soldier-arguments in favor of P or A because they're well-equipped against this opponent, and not because they're the best and soundest and strongest according to objective (read: your) standards.
Here's a related story: in my midterm paper for my Plato's Republic class, my thesis statement was "Plato's position on falsehood in the kallipolis is inconsistent". Bam! Plato would have a heart attack! Dreaded inconsistency! But after I got comments back, I agreed with the professor that what I'd really shown was something weaker: "Plato has good reason, by his own lights, to reject the Noble Lie". No utter logical malady infects his city so thoroughly that I can demonstrate a rejection of modus ponens on the subject at hand. But the revision... is still pretty strong. Inconsistency is a general, powerful case of having reason to reject something. Inconsistency brings with it the guarantee of being wrong in at least one place. But so too, in a gentler and narrower way, does having reason to reject something by your own lights, even if it's not an airtight reason. And this gentleness is more non-threateningly persuasive, and this narrowness demands less background from your interlocutor in logic, and beginning from this preexisting background saves more time, than beginning with a priori principles and proceeding from there to proposition P or action A.
The girl at the bus stop began by having nasty suspicions that doctors are twisted creatures who all walked straight out of an ethics textbook, evil consequentialist plots devoid of professionalism or commonsense morality fully-formed in their minds, and who would see her ambulance-borne self as a sack of valuable organs they could use to salvage numerous other lives if only they made the slightest wrong twitch with a scalpel. But even if we grant that falsehood, she still does not have adequate reason to withdraw her consent for organ donation, as long as she can present proof to evil consequentialist doctors that she's worth more alive than dead. And she can.
Offering arguments like this - ones which use premises you don't hold that opponent does, and which aren't reductios in form - is only dishonest if your conclusion is meant to be, "Objectively and all things considered, you should perform action A or believe proposition P." Those arguments (assuming the premises your opponent holds and you don't are false) show nothing of the kind. But pointing out that people have reasons by their own lights to believe P or perform A - concluding instead "given these premises which you accept, A or P is reasonable" - is not, I contend, underhanded. Conveniently, it's also not slow, mean, or difficult. And maybe these light arts saved a life today.