"simplistic ideas" is a correct and usable phrase in written English.
You can use it to refer to a set of ideas that are too simple or basic to be useful, or ideas that are presented in a simplified way. For example: "He had no real answers, just a bunch of simplistic ideas."
The president himself has "simplistic" ideas.
She hopes to dash simplistic ideas with her new film, "Qaddafi's Female Bodyguards: Shadows of a Leader".
Simplistic culling rarely has the effect that those with simplistic ideas about culling seem to think it will have.
While recognising the concept of a struggling Muslim community or umma that is oppressed by the generic foes of Islam, he finds such simplistic ideas inadequate.
But contrary to simplistic ideas about catty, back-stabbing women, feminists don't fight each other because women are uniquely competitive or cruel.
"The danger is that we will apply overly simplistic ideas about technology and tear apart the institution before we really know what we're doing".
But the simplistic idea that hiring overtly black-hat folks will increase your security is clearly a myth".
We thrill to the "Lincolnesque realism" of John F. Kennedy, who "renounced the simplistic idea of a 'Pax Americana' " by calming the fears of Soviet leaders.
Ultimately what gives the film its credibility is that it avoids any simplistic idea that Iraq could have simply been "got right".
Yet Mr. Hunter also makes it clear that Charlie is willfully eating himself to death out of despair over his lost love, reinforcing a simplistic idea about a complex problem involving both metabolic and psychological factors.
Mr Fortuyn, on the other hand, was demanding a ban on further immigration (with Muslims unpleasantly singled out), a simplistic idea but one shared by many supposedly respectable governments across Europe.
