The first problem here is that nutrition science is a very young field. Yes, some will disagree with this, but it is true. Some examples follow:
Glycemic index is not what really matters. Glycemic index does not account for the amount of a carb that is consumed. What really matters is glycemic load. Glycemic load does account for the amount of the carb. The reason this matters is that glucose has a glycemic index of 100, whether you have one gram or one hundred grams of it. Glycemic load allows a person to quantify the impact a specific amount of a given type of food will have on blood sugar.
The fiber thing is almost useless to argue about. Fiber is almost never considered in the math, because we have almost no understanding of how fiber affects glycemic index. What this means for Soylent is that we can say, “The fiber will counter the glycemic index of the maltodextrin,” but we cannot quantify how much it actually helps. There is evidence that it helps, but so far there is no research that agrees on how much it helps.
As far as research goes, like I said, nutrition science is a very young field. Much of the research is conducted very poorly, because we do not actually know all of the possible confounding factors, and most of those we do know are difficult or impossible to control. Some, like individual biology, are impossible to predict and may even be impossible to account for. What this means is that studies require absolutely huge sample sizes to have even the slightest amount of accuracy, and even that may not be enough. Further, few nutritional studies even follow good scientific method. For instance, a study often cited to claim benefits from drinking red wine turned out to have included a significant number of people in the control group who did not drink because of health problems that may have been caused by drinking. This presents two problems. First, including more people with health problems in the non-drinker group than in the drinker group made the study artificially favor drinkers from the outset. Second, these were people who already had health problems from drinking, and they were being included in the non-drinking group. Ultimately, the conclusion that red wine improves health had to be thrown out because of how poorly the study was conducted. In spite of that, I hear or read people citing the study as showing that red wine is good for health at least 5 to 10 times a year. (There have been similar studies related to drinking coffee. Yes, it turns out coffee has antioxidants, but all decently conducted studies have found that the high antioxidants do not make up for all of the harmful chemicals contained in coffee.)
The best policy is to wait for consensus among the nutrition community. This is not a perfect strategy, but it is better than taking every study at face value. Sadly, the red wine thing is actually the current consensus among the nutrition community, even though it was not valid. This is because the conclusion of the study was popular. Often, even scientific communities can be seduced by being told what they want to hear. The only solution to this is to do some research of your own, in addition to finding the community consensus. Do not accept the conclusions of research because you like how it sounds. This is your health you are toying with. Is your health really less important than feeling good about choices that may be wrong?
Lastly, do not argue about things you know nothing about. I see a lot of comments here on both sides, saying that various things are healthy or unhealthy. Most of them are not backed by any evidence. Sucralose has not been proven to be significantly harmful to health (it has not necessarily been proven entirely safe either; note that aspartame has been shown to be significantly harmful). Excessive sugar intake has been proven to be significantly harmful to health (some nutritional scientists are advocating for excessive amounts of sugar to be considered poisonous even), but the exact quantification is not established. Fiber has been shown to temper the effects of excessive sugar (when taken together), but again, no quantification has been established. Similarly, it has been shown that the body handles pure chemical nutrients differently from those found in natural food sources. There is only quantifiable data for a small handful of these (and indeed, the recommended daily intakes and the tolerable upper intake levels from the IOM are mostly based on pure chemical nutrients, not natural sources). So no argument about the difference can hold, because we have no clue what the difference is on a nutritional level. One thing is certain though: Sucrose is a pure chemical form of carbohydrate (regardless of the source). This is also true of maltodextrin and glucose. All of these are dangerous taken in excess over long periods of time (in fact, if these were your only source of carbs, they would still be harmful taken only in the amounts necessary to sustain human life). Fiber can improve the situation, but we do not know by how much. The point is, there is one pure chemical nutrient that we know is straight up harmful in its most pure forms. It would be reasonable to assume that all other pure chemical forms of nutrients could carry similar risks. This does not mean you should avoid them. It might be wise, however, to take more natural alternatives when possible (for instance, oat flour is a better option than straight maltodextrin and some kind of powdered synthetic or purified fiber). (Note that this is one place where Rob was wrong. There may not be significant evidence that synthetic vitamins are harmful, but lack of proof that something is true is not sufficient to prove that the opposite is true.)
The point of all of this is that we do not know enough about this subject (even the experts do not) to justify heated arguments about it. There is risk associated with any major change in diet, and maybe it is justifiable to argue about whether this particular risk is worth it or not. Beyond that, everything else is just opinion, because the facts are not yet known. So quit treating opinion like fact. It is not!