Even assuming that you could learn "exactly what wizards could do," it wouldn't be just a matter of "cleaning house." Wizards have the power to become completely invisible, look like anyone, control anyone (muggles would be more vulnerable to the Imperius curse than wizards, as very few of them have any training in defending against magical mental attacks), and heal from the most severe wounds in minutes. More likely, if a modern military was able to learn all that, they'd become extra cautious and paranoid.