This is good advice for an individual and relatively useless advice when given to society as a whole. Yes, people should think for themselves. If you have kids you might even be able to teach them how to think for themselves.
But at scale, at the level of a population, an expectation of individual rationality loses out to the realities of these manipulative techniques. On an individual level they might not work, but on a population level they tend to work.
If a population is being manipulated by political propaganda, then yes it's good advice to an individual to think critically / rationally. But that only affects change on the tiniest margin. The propagandists will still win overall.
I think on top of your points, the effect of decades of underfunding education - and on focusing on "marketable" skills over "soft" skills such as critical analysis - must be taken into account.
Why would education matter here at all? People are much more highly educated nowadays than they used to be. They even score much higher on IQ tests compared to people in the past. People understand the world better today than before.
But at scale, at the level of a population, an expectation of individual rationality loses out to the realities of these manipulative techniques. On an individual level they might not work, but on a population level they tend to work.
If a population is being manipulated by political propaganda, then yes it's good advice to an individual to think critically / rationally. But that only affects change on the tiniest margin. The propagandists will still win overall.