you are missing the point. the juubi while it did want it's chakra back, also caused destruction. i caused chaos across the land destroying everything in it's paths. also, it wouldn't have just attacked kaguya, but the sage and his brother too. remember they only have chakra because of the chakra kaguya got from the shinju. when the tree takes it's chakra it also kills you has the chakra becomes part of your life force. there was really no choice other than too stop it. but lets say they decided to sacrifice their family to the juubi and give it back it's chakra, how would they be certain it won't decide to continue it's rampage? so no, the sage was not power hungry. he even states that one person shouldn't be too much powerful than everybody else.