Pretty interesting! I think your message is conveyed pretty well no matter which path the player chooses (thanks mainly to the conversation with the Turbalien), but I agree with your testers that the experience is somewhat hurt by having to quit the game to “win.” People might not make a strong connection between pressing the “End War” button and making a conscious decision to do more than exit a game. When I pushed the “Start War” button, I didn’t think I was making a decision to start a war, just to see what the game had to offer.

Requiring the player to quit removes your chance to inform people about what they can actually do. After not killing the Turbalien and seeing the conversation, a menu could pop up that asks the player if they want to end the war. This would scroll the images and text that you see under the Turbalien-killing scenario (I think all players should see it!) and it could also display some additional information, or links to contact the appropriate government officials and/or action groups.