simple-minded 
adjective
Having or showing very little intelligence or judgement: simple-minded theories he is a simple-minded minion...
- Because they work on simple-minded theories and are totally oblivious of facts.
- But these non-newsworthy-factoids have spawned appallingly simple-minded reflections.
- No amount of simple-minded faith will change that.
Derivatives
simple-mindedly
- So, I asked simplemindedly, is life better or worse since the fall of Ceausescu?
- He subsequently proved himself simplemindedly optimistic.
- However, she still had chosen to simplemindedly follow Cindy.
simple-mindedness
- In a bunk house filled with other rootless job-seekers, Lennie's burden of simplemindedness leads him to commit a hideous crime.
- Hero's plotline is simple to the point of simplemindedness.
- As I look back at those old strips, I see some pretty dumb simplemindedness.