Why do arguments become hostile?

When conversations go wrong, there's a moment right before it gets bad that something must have changed. What is it? What causes the transition from civil to adversarial?

I can think of three reasons, but I'm sure there's more:

Someone feels they are not being heard. When we feel we're not being listened to, most of us get louder. And if that doesn't work, we get louder or more hostile, since we are seeking recognition more than anything. A negative feedback loop ensues, where each person tries to be heard by getting louder, causing the other person to do the same.
We confuse our identity with our point of view. An attack on an idea is not an attack on a person, unless that person can't separate the two. Even if someone makes fun of another person's point of view, is that necessarily an attack on their person? It is if they can't separate themselves from their ideas. If I like blue, and you like green, who cares? Is there a name for the line in each of us between opinions we defend personally (abortion), and we don't (favorite color)?
Cultures where walking away, being polite in the face of idiocy, is seen as weak. Arguing with someone who isn't listening doesn't make much sense. The wise thing to do would be to politely leave, but that's often seen as giving in. The result is people won't relent.
There is an unspoken argument. A previous debate has left unexpressed feelings in one party who insists on trying to vent those feelings from some other exchange during the current conversation. This inevitably makes the other person feel like they're not being heard (#1).
There is no trusted mediator. There is always a third party that can be found that is trusted by everyone, who can step in and restore decorum. Without that third party, negative feedback loops can start and there's no one who can step in to end them.

What are other causes?

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