I went to see a movie today, a character in it made me think about why it is so hard to change other people.
We all probably heard that children are more open to outside effects and we're all probably aware that what you feed to a child's brain makes a bigger impact on their personality in comparison to adults.
I thought about what the difference really is. I think an important factor is that the parents can determine what their children spend their time with, while adults more or less decide themselves what they want to watch, read etc... They've got no authoritive guide so to say.
So once a "deficient" adult is created, approved as an adult and given the permission to lead their own lives then there is probably no turning back. It is unlikely that such a person can make the correct decisions to better themself*, even with seemingly sufficient amount of external influence. While it is easy to change a child's mind with relatively little amount of exposure to new information.
The brainwashing("informing") needed to change a person increases as the person gets older, because the competition of information in the brain also rises. But note that changing some key views in the brain can result in accelareting the process through chain-reactions, by motivating the person to want to change themself would spare some work for example.
(See also this post to understand why the competition is really needed and why you can't just persuade people by simply using rational arguments.)
In the end, one thing becomes even clearer; as long as so much garbage -in comparison to nongarbage- will continue to be pumped from various sources into people's minds, you can't expect a significant foundational improvement in human reasoning. The negative brainwashing has to stop as soon as possible and the "authorities" should proceed with productive, useful brainwashing.