I have observed two classes of people use this dictum frequently.
1. Class who are really ignorant
2. Class who call themselves 'intellectuals'
The former group of people comprise of illiterate people, the oppressed, children, who don’t enjoy the privilege to learn, forced by the circumstances in which they exist. They live in a world of their own. They Work hard during the day and wash away their worries with a goodnight's sleep. Global warming, Terrorism, War, etc don’t distress them. They are ignorant and they enjoy the bliss of not knowing.
The latter group of people claim themselves as 'intellectuals'. They believe in what they think strongly. Refrain from arguments, obstinate about their ideas and bawling out at other's ideas. They are continuously engaged in the process of understanding the truth within themselves. When questioned why they don’t use their knowledge for the up liftment of society, they say 'ignorance is bliss'. They are ignorant and they enjoy the bliss of knowing.
Note: All intellectuals are not ignorant.