Peas, I think you've got a good point, but I think there's another facet to this particular topic. It seems like there are basically two categories of people, when you have incomplete information: those who are comfortable extrapolating from the facts we have, and those who are not. I think that people comfortable extrapolating are rather in the majority, but the problem is that they don't always agree on what facts can be extrapolated, and how far.
So for instance, if you have a woman getting into a car with a car-seat, one poster says that you can't assume anything about the situation at all. A second poster says that you can assume it's her car, but not that the car seat means she personally has children. A third poster says that you can assume it is her car and that she personally has at least one child.
None of these posters will agree with each other completely, even though 2/3 of them are making deductions based off of what we know. 2 of the posters will think that at least one other person is making an unfair assumption. 2 of the posters will think that at least 1 person is being unreasonable for calling it an assumption instead of a deduction.
I think this type of disagreement in what's appropriate actually becomes less obvious with more complex situations. There are enough ways to disagree about interpretations that it's more difficult to see that you at least agree it's reasonable to extrapolate the facts into those various interpretations. Plus, you're more likely to have posters who have opposing viewpoints based one extrapolating the same facts to the same degree...but in different directions. They will not always see that they are reaching their conclusions via the same method, and you can sometimes get a situation where they both think the other is making a lot of unfair assumptions.
I do agree with Jan74, though, that the best rule of thumb is to keep explanations as simple as possible. Extrapolating one fact to reach a conclusion is a very different sort of exercise than extrapolating all but one fact to reach a conclusion. And in situations where it just isn't possible to reach any sort of conclusion without extrapolating a lot of the available information (generally because there isn't much information available), I think it's often better to just avoid discussing that which we cannot ever know for sure.