In any political debate there are two currents underpinning each participant’s position: the preference-based one and the factual one. These aren’t typically distinguished very carefully, but they exist anyway. For instance, one could hold that more immigration from Latin America is desirable from a cultural point of view but that the economic absorptive powers of US society are not sufficient to support it. Or one could hold that it is both desirable and possible for the US law enforcement system to prevent large numbers of people from consuming some illegal drug. Etc, etc.
Not only is it important to separate these admittedly related currents, but it’s important to remember that different people and different debates are guided by different proportions in underlying justifications. It’s probably true that somebody, somewhere is guided by one exclusively without regard to the other, but in most cases these two exist side by side.
Especially since getting to graduate school I tend to rely less on (my-own-)preference-based justifications for my positions and more on factual ones. Obviously, there is still room for debate no matter which part you choose to rely on more; it could be that I have incorrect beliefs about facts, however much I try not to, and I could debate with somebody having the same preferences I have about alternative means of realizing them. The Affordable Care Act is a popular subject of these kinds of debates—I think most people probably want affordable, quality health care to be available to large numbers of people, but there is considerable room for disagreement about whether the ACA is an efficient way to accomplish this.
I don’t mean to slight preferences by saying they are all beyond rational investigation. Philosophy informs (creates?) our preferences, and to the extent that philosophy is about discovering truth, there is room for debate on correct positions. But this is not what I’m expert in, so I don’t make a habit out of it.
It shouldn’t automatically be cause for suspicion when preferences and factual suppositions point a person in the same direction. In fact, it’s probably the exceptional case in which they don’t. But in the interests of intellectual honesty it’s important to make the distinction so we know what we’re talking about and why. And in the interests of strategy, of “dialogue”, it’s important to remember that other people may not use the two threads in the same proportion that you do. Not only will this help you get to the root of the problem quicker, but it will help you from seeing the world like a medieval morality play in which every conflict is good vs. evil. Related: Which Side Are You On? Robert Wolff, Murray Rothbard, and Me by David D. Friedman.