Anger isn’t always bad for a relationship. It is bad for your health, debilitating, and dangerous. It does make you dumber. Like substance abuse, it clouds your judgment. But still, sometimes, a burst of anger can have some benefits.
Like a thunderstorm, it can clear the air. 
Like the clutch in a manual transmission, it can pull tightly meshed metal things apart so they can adjust, change, and reengage; so it changes gears.
It can pull things that are too tightly wound apart, so they can adjust, reposition themselves, and come back together in better alignment.
The aftermath of anger can be a readjustment that ends up for the better.
Not that I’m in favor of getting mad at somebody; I’m not. I’m just saying that the anger cloud can sometimes have a silver lining. I’ve seen some situations in which the cleared vision, the changes that came from anger, were good.
Even in those cases, looking back, it’s too bad they didn’t just go straight to the adjusted vision without suffering the anger first.
(image: tizz66/Flickr cc)
Anger can be an incredibly strong and powerful catalyst for positive change. Just because you’re angry doesn’t mean you have to cause other people pain. You can use it in a more controlled way to get a point across.