if he's going to complain that they're not following the Geneva Convention, he should do so himself

By their very nature, those people are illegal combatants. The idea of illegal combatants was not invented to persecute civilians who take up arms but to protect civilians that choose not to and to safeguard all civilians from the direct action of military force. Here is a link that explains how it works and why it is important. If you want, you can skip to the second to the last paragraph and get the gist.