Because logic is subjective. Not symbolic logic, of whose ineffectuality you lament, but rather the machine in each person processing information through values

Because logic is subjective. Not symbolic logic, of whose ineffectuality you lament, but rather the machine in each person processing information through values and experiences to produce ideas and actions: your logic is not another's. Some may disagree with my calling this "logic," preferring a mathematical approach, but it is a useful definition if the goal is persuasion rather than purity. If you can learn how a given person's logic works, you can generally feed them the inputs necessary to produce the desired outputs. Some may find this immoral, and they may well be right in certain value systems, but they are also needlessly hamstringing themselves to bask in self-congratulatory failure while their opponents likely have no similar scruples. It's utilitarian, to be sure, but I'd happily mislead people to prevent genocide, just as some readily mislead the public to cause genocide. A shortcut for working this angle, especially en masse as we see in political debate, is taking advantage of the many identified cognitive biases.