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.