Kaguya ate the fruit.
This caused her to unleash the hateful juubi but it also let her bear the so6p.
juubi=curse of hatred , so6p=will of fire
you see...2 effects for eating the fruit
The so6p then sealed the juubi to save humanity.
so6p+juubi=curse of hatred and will of fire in 1
The so6p then had his 2 sons while hosting the juubi.
Older son=Juubi's curse of hatred.
Younger son=Sage's will of fire.
So basically what im trying to say is ALL uchiha's are destined and stuck with this curse of hatred. The reason an uchiha was the one to bring the juubi back is because the juubi and them share the same hatred.
The only way i see of ending this cycle is to give the juubi back what was rightfully his..all his chakra...ORRRR...kill off ALL uchiha's so that there may be no one else to bring the juubi back into this world.