I think the deniers are ignorant of the current curriculum being handed out in schools all across the western world. The goal of keeping the populace dumb starts in schools and a percentage of the older population. This has been going on for a few decades now. They want stress free educational environment which aims to reduce any challenge to the student.
Any indoctrination is completely effective on those who are either naive or ignorant compared to those who are much older who know and have learned of the world we live. If you haven't noticed our western world is being taken over by millennial crazies using contradictive and violent means in which to force others to think like them. If you don't think like them or stand with them and their agenda, you're attacked and viciously mobbed socially and physically.
This is this generation. What do you think will come from the next indoctrinated generation?
As scary as it sounds, I think it is a goal for the government of any country to kind of keep the general populace a little naive. I think the less the people are aware, the more the people in power can implement their beliefs and political views in the system.
No, the government is not trying to keep the people of a country dumb by any means. they do have some secrets that it would not be safe to tell, but they try to fill in the public on all of the things that the can and that they should.
Some people in government do try to keep people dumb. Other people in government do not, because they know that it is a lot easier to fix the country by having a knowledgeable populace. The only people that like a dumb populace are the people that get rich off of people's ignorance.
When you put government in the hands of the people, government will inevitably attempt to control the will of the people. Keeping the people "dumb", or otherwise in the dark, makes them too unpredictable. Ignorance is only the first step in controlling the public. A man is more predictable, and therefore less dangerous, if he is sure about something wrong than if he is unsure about something right. The goal of modern governments is not to uninform, but to misinform.
While it may be in the best interest of the Government for it's citizens to not pay that much attention I don't believe it's the goal of any Government to actively keep it's citizens dumb, I think most citizens care very little about politics or many other political topics in general they are only concerned about what effects their day to day life.