The principal target of a blockade is civilians. If they starve to death that's just? If they are killed by another means that's unjust?
Where did I say that dropping the atomic bomb was unjust? It’s not. Japan killed millions of Chinese civilians. Japan had about as many civilian casulties as Romania, even after the atomic bomb drop. Axis civilian casulties were only 4 percent of the total deaths, and most of those were German.
Germans tried that at Leningrad, ultimately didn't work out for them, even though over a million Russians starved to death.