I’m think you’re missing the point.

You face three choices:

1. Most death and harm, 50% chance of happening
2. Less death and harm, 50% chance of happening
3. Principled choice for no death and harm, but that practically makes choice 1 more likely to happen because it has 0 chance of happening.

Choosing choice 3 is equivalent to choosing choice 1 because you’re contributing to choice 1 happening practically.

Choosing choice 3 is directly creating more death and harm than choosing choice 2 and in that way is morally worse.