Howling:Macra uprising in The Macra Terror-Unfair?

The Second Doctor story The Macra Terror seems wrong to me. The humans colonized the Macra's home planet and made it their own. The Macra simply wanted the humans to pay. For all we know, the humans had made the Macra their slaves and so they got a taste of their own medicine. It just seems wrong of the doctor to take the humans side as usual and destroy all the macra when it was their planet first and the humans are the evil invaders. Why does the doctor stop every invader to earth but when it's a human who is invading, he tries to rationilise their actions. He shouldn't be as biased as that towards humans.