So everyone knows that we're supposed to strive to be logical because.. well, it's the logical thing to do. Emotions lead us astray. We have to be constantly on guard against appeals to emotion - since they're evil and bad and manipulative and bad. Right?
Wait, hold on a minute. I mean, of course people get emotional tunnel vision and are mind killed - and of course you gotta not do that, but there's a bit of a baby-with-the-bath-water thing going on here. So called "fallacies" are bayesian evidence. Emotions weren't created by lucifer to tempt us. Our emotions are a part of our brain that has empirically proven to be helpful for things like not dying. We use them to think. Our aim should be to use them well.
Not only is emotional "abstinence only" education fairly ineffective, but it's not really what we want. Do you really want to live a life without passion? Without happiness? Of course not. Emotions are a big part of our life, and they damn well ought to be. And since changing your mind is important and you want to feel rational, emotional appeals are a necessary part of life. Not "necessary" as in "no way to exterminate this evil", but necessary like your liver.
Again, of course, they can be done wrong - and with malicious intent. You should avoid emotional tunnel vision because your System 2 is important too, and anyone aiming to exclude it can be rightfully accused of using the Dark Arts. And overt emotional appeals aren't necessary if you've mastered the skill of taking ideas seriously - if you make sure to translate abstract thoughts into effective emotional appeals internally. But it has to be done. Or else you make predictably bad decisions - whether you're the guy who knows he "should" give up smoking, yet doesn't - or the girl who stays in a relationship that she "knows" is bad for her.
So don't dismiss things for having an emotional component. Don't even dismiss things because they have a strong emotional component and were clearly designed that way. Just make sure you ask for System 2's input as well. Make sure they agree. It ain't the Dark Arts unless they're appealing to your emotions to the exclusion of logic.
If you want to be compelling, you have to get emotions involved. If you use leading language and social pressure to try to force a particular choice - congruency be damned - then you can call it the Dark Arts. If you only pull up some emotions while trying to keep others suppressed/unrealized, then you can call it Dark Arts. However, if you're bringing up all the relevant emotional factors and in clean language just asking "with all that on the table... what do you want?" - so that they're free to answer with no hidden pressures - then you're just helping them find out what they congruently want upon reflection (the horrors!).