I think the problem is the generalization. It depends on the food. Watermelon is surely not comparable to trail mix. Also I have my doubts about the idea that berries are a problem and a mash to squeeze out the water is better than eating them because of the skins and seeds... that makes no sense. The way your intestine absorbs water is different through its length, the first part of the small intestine is what needs dilution of food with juices from liver, intestines and pancreas, to bring it to the same osmolarity of blood, that to allow absorption from that part of the gut, the food will already have an high percentage of fluids when it arrives there due to saliva during mastication and stomach juices. (BTW some sport drinks talk about osmolarity etc saying that an highly concentrated juice will sit in your stomach until diluted and that's not true, the stomach doesn't take care of that).
The final part of the small intestine and the colon work a bit differently as they can absorb fluids against osmotic gradient so they don't need that dilution, by design when the food gets to the large intestines will have lost the majority of the fluids, something like 80/90% and the large intestine will absorb more if necessary (it usually does as there's very little fluid in normal feces... obviously diarrhea is a complete different situation).
Seeds and skins that are not digested don't need liquids, you can't dilute something that has not been destroyed by digestion, and you don't need to, they get pushed along and eliminated. I find odd that with the reason of pushing out a few seeds someone would skip the chance to add whatever nutrition could get from the fruit. The way I see it is that mashing and squeezing is done way more efficiently already by our body and the precious fluids I would waste squeezing a bit of berries by hand would be more important than the bit of fluids temporarily added to it by the body.
For the constipation thing... well the more the feces stand in the colon the more water is absorbed from them, it's not that one gets constipated because the colon can't push the waste along because is too dry, it's perfectly able to push that food out, it's not sand. It takes a long time for an otherwise healthy but constipated person to develop the kind of fecal impaction that would lead to a blockage.
If the idea is that the water is not wasted as it gets absorbed anyways but the process is a problem while the food passes through the first portion of the small intestines where it could be diluted then one needs to figure out the advantage of paying the price for that short time, and in that case quantities of food ingested have their importance as extra dilution of an handful is different than dilution of a full pot of food.
A huge portion of our daily fluid intake comes from food, you can't just cut that out because "it's gonna need dilution" without taking in account the types of food available to you, the total quantity you eat and how you spread that food intake through the day.