One thing I learned a while back is that writing to vent frustration or anger is – for me, of course – a bad idea. In the past I did write a few times to “put somebody in their place”, or to prove with my work that what others claimed was wrong.
The stories sucked.

This is because, I think, no matter what the main engine of our writing is – I have friends that write to keep sane, or to leave behind a reality they find oppressive and explore alternatives, and people that writes just because it’s fun, or it’s the only thing they know … no matter what the nature of the impulse that pushes us forward, we cannot have anything else in our mind but the story.
If we write for ten minutes, in those ten minutes we need to be into the story, without distractions, without second purposes or agendas but to write the best damn story we can.

Writing is a process, a craft, a set of behaviors.
But we need to sort out our priorities.
Writing out of anger can happen, but it does not work if the anger is not focused on the story. If we’re focusing on someone, if we are keeping it small-scale and personal, it all goes pear-shaped.

Which probably means writing should be a form of transmutation – we come to it with our load of anger, anguish, sadness, fear or whatever, and by passing through the story, through the writing process, we make it less personal, less limited. We leave those emotions behind, strip them of their power on our life. We look at these emotions with clarity.

Or something.
Bottom line: never write angry, or if you can’t avoid it, direct your anger at some universal injustice.