There are Witnesses with all levels of intellectual capability. Some are genuinely thick but most aren't even if they are not highly educated or even academic.
Plenty of Witnesses have well paid, white collar jobs that are far from menial roles. Plenty have good businesses. I have know plenty enough who read lots, are interested in the arts and culture, have a reasonable knowledge the sciences and so on.
What most mentally in Witnesses lack however is the willingness to question and investigate beyond the boundaries set by the WTS. For some this is an intellectual challenge for others it's the application of cognitive dissonance.
For example, a Witness may have an interest in the sciences and the intellectual capability to understand some complex aspects of physics, chemistry and biology yet simply discards all the material that presents a worldview contrary to the simplistic world of the Bible. They are conditioned to replace nagging questions with an approach of "leaving it to Jehovah". What's worse is some go further and employ pseudo intellectual nonsense to make it seem like they employed critical thinking skills and are not simply dismissing things without serious thought.
This can be considered "wilful ignorance" but for most it's simply cult conditioning that they really don't question. Like an addicted alcoholic they don't realise they have a problem and it's only when they wake up to that fact that they then make the choice to remain wilfully ignorant or seek to change their behaviour when confronted with information contrary to their JW viewpoint.
