You’re rolling too many things into one here. The concept that fat makes people fat as a direct consequence is false, but only if the calories gained from that fat are reduced elsewhere. Fat contains very dense calories, so consuming fat can lead to too many calories which leads to getting fat. That is not to say that a diet should be devoid of fat and replaced with sugar, just that the overall diet needs to be balanced with both, and not exceed the number of calories required. Any amount of “glugging down sodas” is certainly a problem, no matter if you’re also getting fat in your diet elsewhere.
On to the milk thing... Your complaint about skim milk presupposes that the whole variety is actually meant to be consumed by humans. By “meant” I assume that evolution has formulated the milk of various mamamals to the offspring of their own respective species. So for that definition of “meant”, how can one say that milk formulated for bovine offspring is meant for human consumption as is? Would not the ratios of fat, sugars, vitamins, etc. be out of balance with what a human needs? Right away, the widespread problem of lactose intolerance in humans, even many babies, upholds this view even a little. So why shouldn’t the formulation of cow’s milk as consumed by humans be altered outside of its natural state?