I agree largely with what you say. Two more explanations:
If you don't understand the great mystery that is a religion, but claim to believe it anyway, you show off how pious you are.
Similarly, not knowing things can show your modesty.
Admitting you don't know something can show modesty. The issue brought up here is pride in ignorance, not the humble ability to admit it.
Sometimes I run into people that have rather strong opinions on some topic, and it turns out that they are basing them on quite shallow and biased information. They are aware that their knowledge is quite limited compared to mine, and they admit that they don't want to put in the effort needed to learn enough to level the field.
But that's not really a problem. What is bothering me is that, sometimes, that declaration of ignorance is expressed with some kind of pride.
This behaviour is noticeable on other levels too, in politics or in the sciences-humanities culture clash.
I came up with several hypotheses which might account for this:
Do you notice this behaviour too? What do you think causes it?
EDIT: formatting, style, grammar