Arguments Are Not Valid Simply Because They Support Your Conclusion
V and I recently shared a discussion in which she mentioned that a friend of hers has purchased a second house and intends to rent it out. I remarked that this was unfortunate, as he was parasitically withholding a property from a family whose need for a first residence far outweighs the utility he'd get from it as his second. V's retort provides an excellent case study in how arguments break down if they are not formulated coherently.
Her retort was this: The landlord is justified in extracting rent from the tenants of his second house because without this rent, he would be unable to afford the mortgage on this second house.
It is immediately apparent that this line of reasoning does not hold up to scrutiny. In fact, you do not need to agree with my conclusion to see it; even if your position is that landlords are absolutely morally justified in their actions, V's defense is not sufficient to demonstrate it.
The problem with this argument is that it is completely circular, attempting to justify a course of action based on the fact that it solves a problem that would not exist if this course of action had not been selected. That is, the appeal to the landlord's need to pay the second house's mortgage is spurious because this mortgage would not have burdened him if he had not purchased the house in the first place. The extraction of rent, in other words, is not a solution to an existing problem, but to a problem that arose after the fact. It is incumbent upon V to demonstrate why this course of action is superior to, say, simply not purchasing the house, which would also "relieve" the burden of the mortgage. To illustrate this concept more concretely, imagine if you came home to find that I had flooded your apartment with water, in the process having destroyed all of your possessions and ruined your furniture. When you ask why I had done this, I tell you that I had no choice but to flood your apartment because the fire I'd started in your living room threatened to engulf the whole building. This explanation does not sufficiently explain my actions; I frame my destructive decision (flooding your apartment) as the solution to a problem (the fire) that did not exist until I had deliberately created it. It leaves unanswered the question of why I put myself into a situation which required me to extinguish a fire in the first place.
The deceptively obvious counter to my argument is that the landlord is justified in extracting rent for various other reasons, such as his legal right to do so and his desire for self-enrichment. The problem here is that doing this is not actually a counter. To defer to these arguments is not to refine V's own, but to abandon it in favor of ones that actually make sense. No matter your opinion on landlords, these alternates rise above V's justification because they are not circular in nature. V's argument should not prove convincing to you regardless of your conclusion because it is not a properly formulated argument, and arguments are not endowed with validity simply by virtue of the fact that they accord with your conclusion.
This observation is far from mere pedantry. When your argument lacks precision and self-consistency, the debate at hand must be tabled while we figure out its actual purpose. Put another way, it was not possible for V and I to continue our debate constructively because we had to pause and figure out the rhetorical purpose of an argument that didn't make sense. If her argument had instead been that extracting rent is morally justified because he has an inherent right to do as he pleases with his private property, we could have discussed the merits of that idea. You cannot, however, discuss the merits of a completely circular argument, especially if half the parties involved don't recognize that it is so. The conversation completely stalls; we are stuck in place, spinning our wheels trying to reach a consensus not about the morality of landlords, which is what we were ostensibly discussing, but about the logical foundation of her argument regardless of how well it supports her conclusion, and trying to see if I can ascertain what other distinct assertions she might have intended to make instead and which can actually be pursued rationally. Imagine if she and I had been discussing the morality of capital punishment, and I asserted that it is justified because the sky is blue. V would be forced to argue with me not about the topic at hand, but about the fact that this argument is incoherent. If I persist and declare that she is merely triggered by my impeccable logic, I would have introduced an impenetrable brick wall to the conversation that renders it completely pointless and frustrating. The only substantive difference between "the sky is blue, therefore the death penalty is good" and "buying a second house creates a mortgage, therefore charging rent to pay the mortgage is good" is that the former is transparently inane, while the latter has a sheen of plausibility as long as you don't think deeply enough about it to realize that it appeals to a solution whose problem doesn't exist unless the solution is selected first.
A debate should involve disagreements about the content and merit of arguments, not their validity. All parties should take care to make sure that their arguments are consistent and rational, if not universally agreeable, so that an exchange of ideas is possible. In the realm of politics, we can't begin fixing Americans' incredible polarization if we're stuck squabbling over the logical form that arguments take.