Yeah there was a choice, and the choice was to either use the tardigrade or condemn the miners to death and further Federation lives once the Klingons gained the military advantage. It was cleafrly stated that all starfleet vessels including discovery were at least 80 hours away from the colony by conventional warp, and the colony would not last that long. Michael was putting the needs of the many ahead of the few or in this case one, the one being the tardigrade. Sacrificing innocent lives to preserve one's values and to retain the moral high ground is actually pretty morally questionable if not outright wrong. Sometimes, the ethical choice is not the right choice. By your own argument, In the episode nothing human, The Doctor should have allowed B'elanna to die so that Crell Moset's research could not be used. This isn't the first time that Starfleet officers have been have been faced with ethical dilemmas and had to take an option that they didn't agree with.