People for whom ignorance is bliss, usually prefer the status quo. For them, the world will go on and be no different from the past. Besides, they believe it's better to trust what has worked in the past.
People who seek knowledge, on the other hand, believe in growth, in human beings' potential for self-reinvention and self-renewal.
Anakin Skywalker is an example of someone who doesn't believe in change. He wants everything to remain exactly the same. He wants even to prevent death -- the most essential fact of life!
Obi-Wan Kenobi, on the other hand, epitomizes a person who is always learning, always growing. So much so that he achieved the ultimate power at the end of his life: the ability to merge with the universe by merely closing his eyes!
To get back to your question, I think there are two kinds of people: some prefer not to know. The other kind of people absolutely want to know the truth, even if it shatters their previous assumptions. They know it's the only way to grow.