I don't understand why any of you think this is 'realistic' . There's still nothing to shoot at. The idea of armed vessels is ridiculous.
It's all hypothetical, that's why

Some people like to have these things sorted out in advance
Technically, one could say there could be rogue asteroids and the like to shoot at*, and I doubt some political higher ups (especially those with military background) would like the idea of lab coats being the one behind the trigger on those weapons.
*Though there are other techniques, but for the sake of argument, lets say that shooting is the easiest, most effecient etc.