Its NOT genocide when its retaliation from someone who tried to genocide you. Thats called justice. Anything Tyrande does at this point is justified.
Its not evil. Again, its justice. Just like putting orcs into internment camps - that was more humane than actually just putting them all through capital punishment. You invade our world, with the intent to kill us all and / or enslave us, you should expect to die if you fail. Prison / internment camps is far greater than how someone like the Forsaken treats their “prisoners”. Remember feeding the poisoned pumpkin to the dwarf? Yeah Alliance doesn’t do that to someone they just captured from the other team.