This post is going to build upon two of my other posts: "Positive Arguments vs. Negative Arguments" and "This Argument is Full of Crap!" Please read both of those (even if you already have), so that the material is fresh in your mind and connections among all three posts can be easily made.
Have you ever played the electronic game 20 Questions? If you haven't, this is what it is. You think of an object and the computer will ask you "yes/no" questions until it narrows down what you are thinking about. If you answer 20 questions, and it can't figure out what you're thinking about, you win. I've tried it a few times, and I've been able to stump it a couple. :) What the computer does is ask questions to get answers. It uses these answers as premises in an argument. Let's say that I'm thinking of something. It asks me if it is an animal; I tell it yes. It asks me if it is fury; I say no. It asks me if it is black; I say no. If it asked only these three questions, and told me that me that I was thinking of a frog, it would be wrong. (I'm thinking of a lizard). A frog does match the answers that I gave (the premises of the argument), but it does not match exclusively. The conclusion that the only thing that I could possibly be thinking about is a frog, is an overstate conclusion.
In my example, the implications of the conclusion are not that big of a deal. However, many arguments (especially in philosophy, science, and theology) have extensive implications. Since conclusions to arguments have implications (some quite important), and a wrong conclusion leads to wrong implications, it is imperative that we avoid overstating our conclusions. Overstating the conclusion of one's argument is something that I have noticed on the rise in many different debates. I probably see it more in normal conversation, and when the conversation turns to politics or theology, it might as well be a debate. Here's a couple more dangers of overstating conclusions.
Dangers exist on both sides of an overstated conclusion. First, I'll start with the side making the claim (Party A). If a conclusion is overstated, it creates many loopholes for undermining the argument. The largest loophole is a claimed exclusive conclusion. The premises in the argument may be true and the logic and reason perfectly valid, but the opposition (Party B) can make the whole thing look ludicrous by pointing out that the conclusion does not follow by necessity (especially if the person posing the argument claims that the conclusion is an exclusive conclusion). It is not very common that the Party B will be gracious enough to point out that the premises are valid or that the logic is sound up to the point of the conclusion; they are more likely to not mention that, because of the fact that their refutation of a single portion (especially the conclusion) makes their argument appear to be more valid to less discerning individuals. This is a danger to anyone making a claim (whether right or wrong) because it gives the opposition ammunition where its not warranted, due to the claimer's mistake.
What is the danger for the Party B of an overstated conclusion? Well, it follows from the description above: the focus of the debate has changed. Party B is now focused on demonstrating that the overstated conclusion is, in fact, an overstated conclusion- that the conclusion is not exclusive or necessary. They are forced into providing a negative argument against Party A. Negative arguments must be handled with care, because they can make the person giving them appear to be personally attacking the other side (even if they are perfectly valid and true). This can throw the Party A into another defensive position, which is even farther from the original focus.
It is very important to recognize when a conclusion has been overstated. It will be up to you as to whether or not to point it out in a debate. When you go after the conclusion as being false (or overstated, in this case), it will appear that you are attacking the person's ability to reason. This will most likely be interpreted as an ad-hominem attack, and you will be on the defense. Unless this can be demonstrated quickly and without assumptions, you might want to avoid it. To avoid these negative perceptions (if you wish to voice your recognition), it must be pointed out that you either agree with the premises or that you are granting them for the sake of the argument. That last part is quite important if you wish to expose subtly overstated conclusions. However, I wouldn't waste time on the conclusion if the premises can be demonstrated to be false quickly and undeniably. Exposing false premises can undermine even the most subtly overstated conclusion. By attacking the premises, you avoid the negative argument on the conclusion all together.
Overstated conclusions not only have a danger in debates, but also in developing a theory or worldview. Since an overstated conclusion can have other possible conclusions, it does not force the person to accept the overstated conclusion. Unfortunately, many people do accept overstated conclusions, and when someone points out the flaw, a dogmatic position is often taken to avoid other possible conclusions. If you wish to hold to the overstated conclusion, then you need to provide more evidence that would exclude other possible conclusions. At that point, though, the conclusion is no longer "overstated" and has much more stability.
The best way to avoid overstating your own conclusions is to ask if your conclusion is the only possible conclusion given the premises. If it is not, add more premises; then ask the same question again. Doing this will strengthen your argument and give you more credibility in debates, because you are not trying to lead an argument where it is not capable of going. It someone does point out that your conclusion is overstated, take the time to understand the critique and counter it (you may have to ask some questions for clarification, but that's okay). If you don't have the time to investigate the critique right then, at least acknowledge that you understand what the person is saying, and that you will respond to it later (but only if you intend to actually respond).