I think one of the drivers of arguments is we are trying to understand something, and the argument is subconsciously a way to not just bash their ideas, but test the strength of our own.

In the effort to create a written response we:

1. Find it takes more effort than we imagined to nail down our views, and describe them well.

2. Often have to adapt our own ideas more than we expected to make a clear description possible. Achieving a "better understanding of ourselves" is almost always a reassuring euphemism for "fixing our own surprisingly under-developed/under-coherent ideas".

3. This puts in a more humble mood.

4. Realize the issue is more nuanced than we imagine, and better assess the depth of conversation that even the most constructive engagement would require.

5. Realize we don't have energy left for that.

6. Feel good about having put our ideas to the test and "understanding them better". So a good place to stop.

The practical need to argue (test our ideas in battle) was real, we just didn't need the other person to have the argument. Their imagined pushback forced us to improve our thinking, probably more than we acknowledge.

When preparing for a race, the best thing anyone can do is tell you your opponent is achieving better times than they are. You will achieve more gains by competing with an imaginary competitor, who always sees all your weaknesses, than a real one who likely would not.