Canary in the Coal Mine
Their advice is effective - I know because my parents used it in raising me. But the overall message is that dreamers have fundamentally different needs than most kids. Most kids do fine with being told to do follow a rule without knowing the reason for it, and being expected to do things they don't believe in to get along. Dreamers don't.
But what if dreamers' needs aren't basically different? What if they're just the 'canary in the coal mine'? After all, the vast majority of activists are probably dreamers, and many of them have insisted on changes that benefit others who never complained. For example, most black people put up with Jim Crow and got on with their lives, while a group of black dreamers fought back. And just because most blacks were willing to sit at the back of the bus didn't mean it was fine for them.
A good illustration of this idea occurs with Kestrel Hath in the fantasy book The Wind Singer by William Nicholson. Kestrel, along with her family, lives in a highly regimented city known as Aramanth, where standardized tests determine your social status and everyone knows exactly what they should be doing and is expected to do it without question. Kestrel is a dreamer, so obviously she has a great deal of trouble getting along with that, and through the course of the story she and her family instigate a revolution in Aramanth.
Kestrel's mother, Ira Hath, is a self-proclaimed prophetess (and another dreamer), and throughout the story she repeats the words 'oh, unhappy people'. She is referring not only to her family, who are indeed unhappy, but to all the people of Aramanth. And she is right. Although most people in Aramanth fit in to the social order and don't complain or cause trouble, they are deeply unhappy and need liberation. And the few who can't put up with the social order are the ones who liberate them.
This is why I get uncomfortable when people talk about dreamers having different needs. It means you don't need to examine the established social order - just make an exception for a few people. For example, children with pathological demand avoidance, who are basically autistic dreamers, react badly to ABA treatment. Since ABA treatment has been proven effective for most autistic kids, this is seen as meaning these kids need to be recognized as distinct from other autistics. However, many autistic rights activists have levelled accusations that ABA is unethical, and that forcing autistic kids to act as normal as possible is harmful to them in the long run. The best way to educate a PDA child is also effective with other autistic kids, and doesn't have the same ethical concerns*.
Treating dreamers like they have special needs seems to me like treating canaries as if they're the only ones harmed by carbon monoxide poisoning. The canary in a coal mine is useful as a signal of something that's also bad for coal miners. Similarly, dreamers often highlight societal norms that are problematic for many people, but tolerable to non-dreamers.
* Note that I'm not referring to the advice Elizabeth Newson has provided, which would not work for a standard autistic kid. I think rather than being indirect with commands, it's a better idea to simply explain the reason behind the command and convince the PDA child that your rule is a good idea. If they trust that you have good reasons for telling them what to do, they'll do it.