Kessler syndrome itself could probably be weaponized as the cheapest superweapon ever. Say you rule over a small country, under risk of invasion by a much more powerful country, that relies heavily on GPS guided missiles, aircraft and ammunition. Probably it would not be very expensive to pick a couple fat satellites at the right orbital plane, blow them with small missiles able to reach orbital altitude, and let the resulting debris scattershot start a chain reaction to take down every GPS satellite in existence, rendering low to medium Earth orbit useless for centuries as a byproduct. Those smart ammunitions would be crippled overnight, forcing the more powerful country to risk old style boots-in-the-ground invasion, with much degraded technical support.
Antisat weapons aren't exactly simple, either, though. It's only been successfully done a few times. Intercepting something at orbital velocity isn't trivial (unless you have the capability to actually launch something into a similar orbit and effect a gradual orbital rendezvous.)
I checked, my reasoning doesn't really apply to global positioning satellites, as they have orbits far outside the LEO, about 20000 km. There's not enough mass there yet to ensure a Kessler cascade. They would have to be targeted individually, a far more difficult task.