You gotta play the game by the same rules as the other side. That is the nature of warfare.
During WW2, the United Staes and its allies killed upwards of 8 million civilians, quite deliberately, by firebombinb, nuclear bombing, and just old-fashed iron bombing, plus artillery, machineguns, etc.
The result was that Germany, Japan, Italy and most of the countries that they occupied are now free.
Yes, you do have to fight dirty to get good results. That is the way the real world is.
