Negative emotions can trigger-start your Life
Indignation and Anger can act as liberators from false ideas
For things to actually change, very often we need something to stirr us up. Something that shakes us from the whole core, telling that this is not right, I don't want to live this way. Sometimes negative emotions can play exactly that part in our path of growth. To be the initiators. To initiate us to change, to think differently, to accept a different reality. To believe in a different truth about ourselves. And to liberate us from the false ideas and perceptions we already have.
So, anger and indignation are not BAD emotions. Just like the positive ones - happiness, calm, joy - they act like a feedback. And they also can act like initiatiors towards change.