People have tried playing exceedingly dirty in the past - colonial powers, especially. It doesn't usually work. Ultimately, unless you're willing to build your own infrastructure, you need to rely on local infrastructure. That requires supporters who won't try and sabotage you at every turn, and report everything you do to the enemy. Building your own infrastructure takes lots of people, money, and time. Successful asymmetric warfare works exactly the opposite way to killing all your enemies - it works by taking a group of your enemies, then convincing them you're the better bet.