Blissful ignorance

I was impressed by your answers to my "lonesome valley" type question. Thanks.

Here's another one. Have you got any good phrases for someone who holds under-informed opinions tenaciously? Or for the act of holding tenaciously to such opinions?

Spark

'Bullheaded,' 'pigheaded,' 'muleheaded,' 'mulish' and 'willful' are mentioned in the archives.

I love a phrase used by Truman Capote. He said someone was, "The most deeply ignorant man I've ever met."

If ignorance is bliss then he is the most blissful person on earth...
SR