Righteous Indignation and Anger

When looking for new friends, seek out those with whom you share positive interests – things you love; be it sports, hiking, photography, opera, whatever.  Over time, you are likely to find other things you love.  These may be woven into the fabric of the friendship, or not, but the foundation will still be the shared interest in the positive – and you will think positively when you think of each other.  

If you instead find friends with whom your shared interest is something you hate, or that makes you angry, you will learn to hate and be angry together.  You’ll meet and spend time with other people who are angry; and that will become your social norm. You’ll associate one another with anger, and will certainly one day will find yourself in the cross-hairs of the other's anger. 

This is not to say that one should never discuss social justice, unmet needs, or things which make us angry.  There is much injustice in the world – much to be angry about. But we need to take care that we not become consumed by righteous indignation, anger, or—further along the slippery slope—hatred.  Once these become a habit, they become an end in themselves, and will not be dislodged by the positive - even if the underlying cause of the anger is resolved.  

Nietzsche had a great take on this:

Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you.