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There are stories of adult children deprogramming their parents / in-laws by blocking these sites via their routers [0], and within a few weeks they're able to see their parents' views and demeanor visibly change for the positive [1].
The post from BestOfRedditorUpdates [1] for example shows the progression, basically the same as the 5 stages of grief, or withdrawal from a drug habit. First they get angry, then they try to find ways around it, then they accept that they can't and start doing something else.
The truth is most people don't really go to these sites out of choice, they do it out of habit. If you can alter the habit, you can stop them from consuming such content. It's no different than stopping any other habit, like (if you're a smoker or alcoholic) not going to places where people smoke for example.
You can also replace the habit with something else; like smokers chewing nicotine gum instead of smoking, or like those trying to lose weight going for a walk instead of sitting at home and cracking open a cold one after a long day of work, this person's aunt replaced it with BTS [2].
[0] https://old.reddit.com/r/HermanCainAward/comments/vb3ddu/rhe...
[1] https://old.reddit.com/r/BestofRedditorUpdates/comments/yz7y...
[2] https://old.reddit.com/r/QAnonCasualties/comments/sis22t/my_...
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I wonder if in this case these techniques might have worked as well.