30's story about space war: Earth ship destroys enemy planet with weapon, only to return to find Earth destroyed by the enemy with the same weapon

Looking for 1930's short story about space war where Earth ship destroys enemy planet, only to return to find Earth destroyed by the enemy with the same weapon. The gist of the story was the debate on the Earth ship about the morality/ethics of using the weapon at all. I recall that the ship had to make jumps that took some time (basically allowed the discussion to unfold on the jump to the enemy system, and the jump back to Earth after deciding to launch the weapon). I'd like to use it for a game engine cinematic plot.